Rapid synthesis method of ZSM-5 molecular sieve with low silica-alumina ratio

Abstract

The invention discloses a rapid synthesis method of a ZSM-5 molecular sieve with a low silica-alumina ratio, and the method comprises the following steps: (1) uniformly mixing a silicon source, an aluminum source, sodium hydroxide, an organic structure directing agent and water to obtain a silica-alumina mixed sol solution; (2) adding a nano ZSM-5 seed crystal, and stirring until the materials are uniformly mixed; (3) transferring the mixture into a tubular reactor, crystallizing, and carrying out rapid reaction under the assistance of the nano ZSM-5 seed crystal by utilizing the advantages of rapid heat transfer and mass transfer of the tubular reactor; and (4) washing, drying and roasting the product obtained by crystallization to obtain the ZSM-5 with low silica-alumina ratio. According to the synthesis method disclosed by the invention, the ZSM-5 molecular sieve with the low silica-alumina ratio can be rapidly synthesized in an extremely short time, and the problems of relatively long synthesis time and the like of the ZSM-5 molecular sieve with the low silica-alumina ratio in the prior art can be solved.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve preparation, specifically relating to a rapid synthesis method for low silica-alumina ratio ZSM-5 molecular sieves based on a tubular reactor. Background Technology

[0002] Molecular sieves are a class of porous materials with silicon-oxygen and aluminum-oxygen tetrahedral basic structural units, widely used in the petrochemical industry. ZSM-5 molecular sieves, due to their unique pore structure, exhibit excellent structural stability and shape-selective catalytic activity. Molecular sieves with a silicon-to-aluminum ratio (Si / A ratio) <30 are called low-silica molecular sieves. These sieves typically have larger pore sizes and higher levels of Brønsted (B) acid, Lewis (L) acid, and total acidity, exhibiting higher low-temperature activity. Therefore, they can effectively catalyze the conversion and decomposition of organic matter and adsorb organic molecules. Low-Si / A ratio molecular sieves can be used in automotive exhaust purification, industrial waste gas treatment, and chemical reaction catalysts.

[0003] The most commonly used method for synthesizing molecular sieves is hydrothermal synthesis. A typical synthesis process is as follows: First, an amorphous precursor rich in silica and alumina is mixed with a cation source under alkaline conditions (high pH). Then, the reaction mixture is placed in a sealed autoclave and heated to over 100°C for a hydrothermal reaction. In the initial reaction stage, the precursor remains amorphous. Subsequently, an "induction period" occurs, during which crystalline zeolite products begin to form and gradually increase in quantity. Ultimately, almost all the amorphous precursor is converted into zeolite crystals of equal mass, which can be recovered through filtration, washing, and drying. The advantages of the hydrothermal method include a mild reaction temperature, fewer crystal defects in the molecular sieve product, and simple operation that is easy to scale up. However, it also has some limitations, such as a longer synthesis cycle, relatively high equipment requirements, and potentially higher raw material costs. For example, synthesizing ZSM-5 molecular sieves with a silica-to-alumina ratio of 25 using the hydrothermal method is difficult, and the resulting products often have low crystallinity and are prone to impurities. This is mainly because the hydrothermal synthesis system with a low silicon-to-aluminum ratio contains a high concentration of aluminum, which causes the precursor to hydrolyze prematurely and the gel concentration to be too high, resulting in the presence of impurities and amorphous silica during the hydrothermal synthesis of molecular sieves.

[0004] In the conventional crystallization synthesis of ZSM-5 molecular sieves, organic amines are generally used as template agents (common template agents include tetrapropylammonium hydroxide, tetraethylammonium hydroxide, and n-butylamine). Patents CN 1715186 A and CN 1247457C prepared ZSM-5 molecular sieves using different template agents. Patent CN1958453A dissolved a silicon source in an acid solution, mixed it thoroughly, introduced a template agent, and then slowly added an aqueous aluminum source solution dropwise to the silicon source solution, while simultaneously adding molecular sieve seed crystals. Hydrothermal crystallization was then carried out at 100–200℃ for 10–60 hours to obtain ZSM-5 molecular sieves. Patent CN85100463 A discloses a method for directly synthesizing ZSM-5 molecular sieves using water glass, inorganic acid, and aluminum salts (aluminates). The method involves a direct reaction of water glass, inorganic acid, and aluminum salts (aluminates), followed by crystallization at 100–260°C for 4 hours to 40 days. After filtration, washing, drying, and calcination, ZSM-5 molecular sieves are obtained. The synthesis of low-silicon-aluminum ratio ZSM-5 molecular sieves is generally complex and time-consuming, with a synthesis cycle of 2–40 days, which is unfavorable for industrial production. Therefore, the rapid synthesis of low-silicon-aluminum ratio ZSM-5 has significant industrial application value.

[0005] Lei, W.; Li, L.; Chen, X., Fast synthesis of hierarchical nanosized pure Si-Beta zeolite with low organic template content via the solvent-free method. Journal of Solid State Chemistry 2022, 308. This report describes the successful crystallization of Si-Beta zeolite within 16 hours with the aid of 1% seed crystals and a low organic template content of TEAOH / SiO2, yielding a product with high crystallinity. Although this method effectively improves the crystallization rate, the crystallization time of the target zeolite is still as long as 16 hours, failing to achieve the goal of rapid synthesis within 1 hour.

[0006] Luan, H.;Lei, C.;Ma, Y.;Wu, Q.;Zhu, L.;Xu, H.;Han, S.;Zhu, Q.;Liu, X.;Meng, X.;Xiao, F.-S., Alcohol-assisted synthesis of high-silica zeolites in the absence of organic structure-directing agents. Chinese Journal of Catalysis 2021, 42(4), 563-570. High silica-to-alumina ratio molecular sieves can be synthesized using a seed crystal and alcohol co-filling strategy in the absence of organic structure-directing agents (OSDAs); however, the crystallization time involved in this synthesis is relatively long (greater than 24 hours), and the silica-to-alumina ratio of the molecular sieves prepared by this method is relatively high (greater than 38). This method still falls short of the goal of achieving rapid synthesis of low silica-to-alumina ratio ZSM-5 molecular sieves.

[0007] Chen, X.; Jiang, R.; Gao, Y.; Zhou, Z.; Wang, X., Synthesis of nano-ZSM-5 zeolite via a dry gel conversion crystallization process and its application in MTO reaction. CrystEngComm 2021, 23(15), 2793-2800. This paper reports the synthesis of nano-ZSM-5 zeolite with superior catalytic performance based on the dry gel conversion (DGC) method. In the dry gel conversion method, the required zeolite precursor dry gel powder is first prepared. This powder contains the silicon source, aluminum source, template agent, and a certain amount of water required for zeolite synthesis. Then, the dry gel powder is placed in a closed reaction vessel, and under the condition of no additional water addition, the chemical reaction in the gel powder is promoted by heating, thereby converting it into a molecular sieve. However, the synthesis of molecular sieves in the dry gel conversion method requires the prior preparation of dry gel; and the crystallization time of this method is relatively long (greater than 4 hours).

[0008] Chinese patent CN 107963639 A discloses a rapid synthesis method for ZSM-5 molecular sieves with uniform nanoparticle size. This method involves rapid crystallization in a metal reactor, completing the crystallization process within 30 minutes, thus shortening the synthesis time of zeolite. However, the applicable range of the silicon-to-aluminum ratio (SiO2:Al2O3) for this method is SiO2:Al2O3 = 1:(0.020~0.0025), which does not meet the industrial requirement for a lower SiO2:Al2O3 ratio. When the SiO2:Al2O3 ratio is further reduced, the resulting product often has lower crystallinity and is prone to the formation of impurities. This is mainly because in the hydrothermal synthesis system with a low SiO2:Al2O3 ratio, there is a high concentration of aluminum ions, which leads to premature hydrolysis of the precursor and an abnormally high concentration of gel. These factors work together to ultimately result in the formation of impurity phases and amorphous silica during the hydrothermal synthesis of molecular sieves.

[0009] Chinese patent CN108178163A discloses a low-silica, multi-level ZSM-5 zeolite molecular sieve, its preparation method, and its applications. The preparation method includes: mixing water, a microporous organic template agent, and an alkali metal until a clear state is reached; adding an aluminum source and continuing stirring until dissolved; adjusting the pH value; dividing the mixture into two parts, A and B; slowly adding a silicon source to solution A and aging it; introducing seed crystals into solution B; mixing solutions A and B and aging them; pre-crystallizing the resulting hydrothermal synthesis system before crystallization; and post-processing. However, this preparation method has a long crystallization time, requiring 24 hours for successful crystallization, resulting in significant energy consumption.

[0010] Chinese patent CN111547739 A discloses a method for preparing ZSM-5 zeolite molecular sieves with a low silicon-to-alumina ratio, employing a hydrothermal synthesis method and using a pre-crystallization solution instead of a template agent. However, this preparation method requires a crystallization time of 32 hours, and its silicon-to-alumina ratio n(SiO2):n(Al2O3) is only <30, which does not meet the industrial demand for ZSM-5 molecular sieves with an even lower silicon-to-alumina ratio (<25). Summary of the Invention

[0011] The purpose of this invention is to provide a method for rapidly synthesizing low silica-to-alumina ratio ZSM-5 molecular sieves in a very short time, in order to solve the problems existing in the prior art, such as the difficulty in synthesizing low silica-to-alumina ratio ZSM-5 and the long synthesis time.

[0012] To achieve the above objectives, the present invention provides a rapid synthesis method for ZSM-5 molecular sieves with a low silica-to-alumina ratio, the synthesis method comprising the following steps:

[0013] (1) Mix silicon source, aluminum source, sodium hydroxide, organic structure directing agent and water evenly to obtain silicon-aluminum mixed sol solution;

[0014] (2) Add nano ZSM-5 seed crystals and stir until evenly mixed;

[0015] (3) The mixture was transferred to a tubular reactor and crystallized, and the reaction was carried out rapidly under the assistance of nano ZSM-5 seed crystals;

[0016] (4) After washing, drying and calcining the crystallized product, a low silicon-to-aluminum ratio ZSM-5 is obtained.

[0017] The molar ratio of silicon source, aluminum source, sodium hydroxide, organic structure directing agent, and water is 1:(0.022-0.033):(0.1-0.2):(0.05-0.15):(5-10); wherein the silicon source, aluminum source, and sodium hydroxide are calculated as oxides SiO2:Al2O3:NaOH.

[0018] The present invention provides a rapid synthesis method for low silicon-to-aluminum ratio ZSM-5 molecular sieves. The preparation process of the nano ZSM-5 seed crystals includes: mixing silicon source, structure directing agent and water uniformly to obtain a precursor solution, aging it, and then transferring it to a hydrothermal reactor for hydrothermal synthesis reaction to obtain nano ZSM-5 seed crystals.

[0019] The rapid synthesis method of low silica-alumina ratio ZSM-5 molecular sieve of the present invention includes a hydrothermal synthesis reaction at a temperature of 160-180℃ for 12-24h and an aging temperature of 80-100℃ for 12-72h.

[0020] The present invention provides a rapid synthesis method for low silica-to-alumina ratio ZSM-5 molecular sieves, wherein the silicon source is at least one selected from silica sol, sodium silicate, silica, silicic acid, and inorganic silica gel.

[0021] The present invention provides a rapid synthesis method for low silica-to-alumina ratio ZSM-5 molecular sieves, wherein the aluminum source is at least one selected from aluminum hydroxide, sodium aluminate, aluminum nitrate, and aluminum chloride.

[0022] The rapid synthesis method of the low silica-to-alumina ratio ZSM-5 molecular sieve of the present invention, wherein the organic structure directing agent is selected from at least one of tetrapropylammonium hydroxide (TPAOH) and hexadecyltrimethylammonium bromide (CTAB).

[0023] The present invention provides a rapid synthesis method for low silicon-aluminum ratio ZSM-5 molecular sieves, wherein the mass ratio of nano ZSM-5 seed crystals to silicon-aluminum mixed sol solution is 1:10-50.

[0024] The present invention discloses a rapid synthesis method for low silica-alumina ratio ZSM-5 molecular sieves, wherein the tubular reactor is 10-15 cm in length, made of stainless steel, and has high-pressure resistant sealing at both ends.

[0025] The rapid synthesis method of low silica-alumina ratio ZSM-5 molecular sieve of the present invention includes the following steps: in step (2), the stirring time is 10-30 min; in step (3), the crystallization temperature is 160℃-210℃ and the crystallization time is 10 minutes to 3 hours; in step (4), the washing is done with deionized water; the drying temperature is 80-120℃; the calcination temperature is 450-650℃ and the calcination time is 6-12 hours.

[0026] The ZSM-5 molecular sieve synthesized in this invention is a low-silica-alumina molecular sieve with a silica-alumina molar ratio of no more than 25 and abundant acidic sites. The rapid synthesis method of this invention effectively improves the crystallinity and purity of the low-silica-alumina ratio ZSM-5 molecular sieve.

[0027] This invention enables the rapid synthesis of ZSM-5 molecular sieves using a tubular reactor. In the tubular reactor, the sol-gel process is accelerated by adding seed crystals, allowing for the crystallization and synthesis of ZSM-5 molecular sieves in a shorter time, reducing the synthesis time to within 10 minutes. This rapid synthesis of ZSM-5 molecular sieves enables applications in industrial catalysis and other fields. Attached Figure Description

[0028] Figure 1 XRD of ZSM-5 molecular sieves in Examples 1-5 and Comparative Example 1.

[0029] Figure 2 The image shows a SEM image of the nano ZSM-5 seed crystals from Example 1.

[0030] Figure 3 The attached diagram shows the nitrogen adsorption-desorption process of the low silica-alumina ratio ZSM-5 molecular sieve in Example 1.

[0031] Figure 4 This is a SEM image of the low silica-to-alumina ratio ZSM-5 molecular sieve from Example 1.

[0032] Figure 5 This is a SEM image of the low silica-to-alumina ratio ZSM-5 molecular sieve from Example 2.

[0033] Figure 6 This is a SEM image of the low silica-to-alumina ratio ZSM-5 molecular sieve from Example 3.

[0034] Figure 7 This is a SEM image of the low silica-to-alumina ratio ZSM-5 molecular sieve from Example 4.

[0035] Figure 8 This is a SEM image of the low silica-to-alumina ratio ZSM-5 molecular sieve from Example 5.

[0036] Figure 9 The image shows the SEM image of the low silica-to-alumina ratio ZSM-5 molecular sieve of Comparative Example 1. Detailed Implementation

[0037] 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.

[0038] Source of raw materials or equipment:

[0039] (1) Tetraethyl orthosilicate, analytical grade, Beijing Innocare Technology Co., Ltd.;

[0040] (2) Aluminum hydroxide, analytical grade, Shanghai Maclean Biochemical Technology Co., Ltd.;

[0041] (3) Sodium hydroxide, analytical grade, Aladdin;

[0042] (4) Tetramethylammonium hydroxide solution, 40wt%, Zhejiang Kent Catalytic Materials Technology Co., Ltd.;

[0043] (5) Colloidal silica Ludox AS-40, 40wt%, Sigma-Aldrich (Shanghai) Trading Co., Ltd.;

[0044] (6) Silica sol, sodium silicate, silica, silicic acid and inorganic silica gel, analytical grade, Aladdin.

[0045] Evaluation and analysis methods:

[0046] XRD results were analyzed using a Bruker D8 ADVANCEX X-ray diffractometer (Germany).

[0047] The morphology of the molecular sieves was characterized using a JSM7401 scanning electron microscope from Nippon Electron Ltd.

[0048] The nitrogen adsorption-desorption characterization of the molecular sieve samples was performed using the Autosorb-iQ fully automated specific surface area and pore size distribution analyzer from Anton Paar (Shanghai) Trading Co., Ltd.

[0049] The silicon and aluminum content of the molecular sieve samples was characterized using an iCAPRQ inductively coupled plasma mass spectrometer from Thermo Fisher Scientific.

[0050] Example 1

[0051] Synthesis of nano-ZSM-5 seed crystals. First, tetraethyl orthosilicate, tetramethylammonium hydroxide, and water were thoroughly mixed to obtain a precursor solution with the following molar ratio: SiO2:0.022Al2O3:0.2NaOH:0.1TPAOH:10H2O. Subsequently, this solution was aged at 90℃ for 24 hours. After aging, the reaction solution was transferred to a stainless steel autoclave and reacted at 170℃ for another 24 hours to obtain nano-ZSM-5 seed crystals.

[0052] Rapid Synthesis of Low Si / A Ratio ZSM-5 Molecular Sieves. Colloidal silica Ludox AS-40, aluminum hydroxide, sodium hydroxide, organic structure directing agent (TPAOH), and water were mixed in a molar ratio of SiO2:0.022Al2O3:0.2NaOH:0.1TPAOH:10H2O to obtain a silica-alumina mixed sol solution. Nano-sized ZSM-5 seed crystals were then added at a mass ratio of 1:10 to the silica-alumina mixed sol solution, and the mixture was stirred for 10 minutes to ensure homogeneity. The mixture was then transferred to a 10 cm long stainless steel tubular reactor with high-pressure-resistant seals at both ends and crystallized in a 190°C oil bath for 1 hour. After crystallization, the reactor was rapidly cooled in cold water for 5 minutes to terminate the reaction.

[0053] Product washing and drying. First, the crystallized product was washed with water until the pH reached 7.5, and then dried at 80°C. After drying, the product was calcined at 550°C for 6 hours to prepare ZSM-5 molecular sieves with a crystal size of approximately 1 micrometer. Its X-ray diffraction (XRD) image is shown below. Figure 1 As shown. Results of nitrogen adsorption-desorption experiments (e.g.) Figure 3 As shown in the figure, the specific surface area of ​​this molecular sieve is approximately 339.875 cm². 3 / g, total pore volume is 0.225cm³ 3 / g, with a micropore volume of 0.123cm³. 3 / g. Scanning electron microscopy (SEM) images of this ZSM-5 molecular sieve are shown in... Figure 4 Compared with Comparative Example 1, this zeolite exhibits higher crystallinity and faster crystallization rate. Inductively coupled plasma (ICP) analysis determined the silica-to-alumina molar ratio of the zeolite to be 24.4.

[0054] Example 2

[0055] The nano ZSM-5 seed crystals from Example 1 were used.

[0056] Rapid Synthesis of ZSM-5 Molecular Sieves with Low Si / A Ratio. Silica, sodium aluminate, sodium hydroxide, TPAOH, and water were mixed in a molar ratio of SiO2:0.03Al2O3:0.1NaOH:0.15TPAOH:5H2O to obtain a silica-alumina mixed sol solution. Nano-ZSM-5 seed crystals were then added at a mass ratio of 1:50 to the silica-alumina mixed sol solution, and the mixture was stirred for 30 minutes to ensure homogeneity. The mixture was then transferred to a 15cm long stainless steel tubular reactor with high-pressure-resistant seals at both ends and crystallized in a 160°C oil bath for 3 hours. After crystallization, the reactor was rapidly cooled in cold water for 5 minutes to terminate the reaction.

[0057] Product washing and drying. First, the crystallized product was washed with water until the pH reached 7.5, and then dried at 120°C. After drying, the product was calcined at 650°C for 8 hours to prepare ZSM-5 molecular sieve. Its X-ray diffraction (XRD) image is shown below. Figure 1 As shown. A scanning electron microscope (SEM) image of the ZSM-5 molecular sieve is presented. Figure 5 The ZSM-5 molecular sieve has a grain size of approximately 1 μm. Compared to Comparative Example 1, it exhibits higher crystallinity and faster crystallization rate. Inductively coupled plasma (ICP) analysis determined the silica-alumina molar ratio of this molecular sieve to be 25.

[0058] Example 3

[0059] The nano ZSM-5 seed crystals from Example 1 were used.

[0060] Rapid Synthesis of ZSM-5 Molecular Sieves with Low Si / A Ratio. Inorganic silica gel, aluminum chloride, sodium hydroxide, organic structure-directing agent (CTAB), and water were mixed in a molar ratio of SiO2:0.03Al2O3:0.1NaOH:0.05CTAB:8H2O to obtain a silica-alumina mixed sol solution. Nano-ZSM-5 seed crystals were then added at a mass ratio of 1:30 to the silica-alumina mixed sol solution, and the mixture was stirred for 10 minutes to ensure homogeneity. The mixture was then transferred to a 10 cm long stainless steel tubular reactor with high-pressure-resistant seals at both ends and crystallized in an oil bath at 210 °C for 90 minutes. After crystallization, the reactor was rapidly cooled in cold water for 5 minutes to terminate the reaction.

[0061] Product washing and drying. First, the crystallized product was washed with water until the pH reached 7.5, and then dried at 100°C. After drying, the product was calcined at 450°C for 12 hours to prepare ZSM-5 molecular sieve. Its X-ray diffraction (XRD) image is shown below. Figure 1As shown. Compared with Comparative Example 1, it exhibits higher crystallinity, faster crystallization rate, and larger particle size. Scanning electron microscopy (SEM) images of this ZSM-5 molecular sieve are shown in [image / description]. Figure 6 The ZSM-5 molecular sieve has a grain size of approximately 1 μm. Inductively coupled plasma (ICP) analysis determined that the silicon-to-aluminum molar ratio of this molecular sieve is 25.

[0062] Example 4

[0063] The nano ZSM-5 seed crystals from Example 1 were used.

[0064] Rapid Synthesis of Low Si / A Ratio ZSM-5 Molecular Sieves. Silicic acid, sodium aluminate, sodium hydroxide, organic structure directing agent (TPAOH), and water were mixed in a molar ratio of SiO2:0.025Al2O3:0.15NaOH:0.05TPAOH:5H2O to obtain a silica-alumina mixed sol solution. Nano-sized ZSM-5 seed crystals were then added at a mass ratio of 1:20 to the silica-alumina mixed sol solution, and the mixture was stirred for 20 minutes to ensure homogeneity. The mixture was then transferred to a 13 cm long stainless steel tubular reactor with high-pressure-resistant seals at both ends and crystallized in a 210°C oil bath for 10 minutes. After crystallization, the reactor was rapidly cooled in cold water for 5 minutes to terminate the reaction.

[0065] Product washing and drying. First, the crystallized product was washed with water until the pH reached 7.5, and then dried at 80°C. After drying, the product was calcined at 550°C for 6 hours to prepare ZSM-5 molecular sieve. Its X-ray diffraction (XRD) image is shown below. Figure 1 As shown. A scanning electron microscope (SEM) image of the ZSM-5 molecular sieve is presented. Figure 7 The ZSM-5 molecular sieve has a grain size of approximately 1 μm. Compared to Comparative Example 1, it exhibits higher crystallinity and faster crystallization rate. Inductively coupled plasma (ICP) analysis determined that the silicon-aluminum molar ratio of this molecular sieve is 25.

[0066] Example 5

[0067] The nano ZSM-5 seed crystals from Example 1 were used.

[0068] Rapid Synthesis of Low Si / A Ratio ZSM-5 Molecular Sieves. Colloidal silica Ludox AS-40, aluminum hydroxide, sodium hydroxide, organic structure directing agent (TPAOH), and water were mixed in a molar ratio of SiO2:0.022Al2O3:0.2NaOH:0.05TPAOH:10H2O to obtain a silica-alumina mixed sol solution. Nano-sized ZSM-5 seed crystals were then added at a mass ratio of 1:40 to the silica-alumina mixed sol solution, and the mixture was stirred for 25 minutes to ensure homogeneity. The mixture was then transferred to a 10 cm long stainless steel tubular reactor with high-pressure-resistant seals at both ends and crystallized in a 200°C oil bath for 1 hour. After crystallization, the reactor was rapidly cooled in cold water for 5 minutes to terminate the reaction.

[0069] Product washing and drying. First, the crystallized product was washed with water until the pH reached 7.5, and then dried at 90°C. After drying, the product was calcined at 550°C for 8 hours to prepare ZSM-5 molecular sieve. Its X-ray diffraction (XRD) image is shown below. Figure 1 As shown. A scanning electron microscope (SEM) image of the ZSM-5 molecular sieve is presented. Figure 8 The ZSM-5 molecular sieve has a grain size of approximately 1 μm. Compared with Comparative Example 1, it exhibits higher crystallinity and faster crystallization rate. Inductively coupled plasma (ICP) analysis determined that the silicon-aluminum molar ratio of this molecular sieve is 25.

[0070] Comparative Example 1

[0071] The nano ZSM-5 seed crystals from Example 1 were used.

[0072] Synthesis of ZSM-5 molecular sieve. Colloidal silica Ludox AS-40, aluminum hydroxide, sodium hydroxide, organic structure directing agent (TPAOH), and water were mixed in a molar ratio of SiO2:0.022Al2O3:0.2NaOH:0.05TPAOH:10H2O to obtain a silica-alumina mixed sol solution. Nano-sized ZSM-5 seed crystals were then added at a mass ratio of 1:10 to the silica-alumina mixed sol solution, and the mixture was stirred for 10 minutes to ensure homogeneity. The mixture was then transferred to a hydrothermal reactor and crystallized at 190°C for 6 hours. After crystallization, the reactor was rapidly cooled in cold water for 5 minutes to terminate the reaction.

[0073] Product washing and drying. First, the crystallized product was washed with water until the pH reached 7.5, and then dried at 80°C. After drying, the product was calcined at 550°C for 6 hours to prepare ZSM-5 molecular sieve. Its X-ray diffraction (XRD) image is shown below. Figure 1 As shown. A scanning electron microscope (SEM) image of the ZSM-5 molecular sieve is presented. Figure 9 The ZSM-5 molecular sieve has a grain size of approximately 1 μm. Compared to Example 1, the molecular sieve exhibits poorer crystallinity and a slower crystallization rate. Inductively coupled plasma (ICP) analysis determined that the silicon-aluminum molar ratio of this molecular sieve is 25.

[0074] As can be seen from the results of the examples and Comparative Example 1, compared with the traditional hydrothermal reactor, the ZSM-5 molecular sieve obtained by the rapid synthesis method of the present invention has high crystallinity, and the synthesis method effectively improves the crystallinity and crystallization rate of the low silica-alumina ratio ZSM-5 molecular sieve and shortens the synthesis time.

[0075] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A rapid synthesis method of low silicon to alumina ratio ZSM-5 molecular sieve, characterized in that, Includes the following steps: (1) Mix silicon source, aluminum source, sodium hydroxide, organic structure directing agent and water evenly to obtain silicon-aluminum mixed sol solution; (2) Add nano ZSM-5 seed crystals and stir until evenly mixed; (3) The mixture was transferred to a tubular reactor and crystallized, and the reaction was carried out rapidly under the assistance of nano ZSM-5 seed crystals; (4) After washing, drying and calcining the crystallized product, a low silicon-to-aluminum ratio ZSM-5 is obtained. The molar ratio of silicon source, aluminum source, sodium hydroxide, organic structure directing agent, and water is 1:(0.022-0.033):(0.1-0.2):(0.05-0.15):(5-10); wherein the silicon source, aluminum source, and sodium hydroxide are calculated as oxides SiO2:Al2O3:NaOH.

2. The process for rapid synthesis of low silicon to alumina ratio ZSM-5 molecular sieve of claim 1, wherein, The preparation process of the nano ZSM-5 seed crystals includes: mixing silicon source, structure directing agent and water evenly to obtain precursor solution, aging, and then transferring to hydrothermal reactor for hydrothermal synthesis reaction to obtain nano ZSM-5 seed crystals.

3. The rapid synthesis method of low silica-to-alumina ratio ZSM-5 molecular sieve according to claim 1, characterized in that, The hydrothermal synthesis reaction is carried out at a temperature of 160-180℃ for 12-24 hours; the aging process is carried out at a temperature of 80-100℃ for 12-72 hours.

4. The rapid synthesis method of low silica-to-alumina ratio ZSM-5 molecular sieve according to claim 1, characterized in that, The silicon source is at least one of silica sol, sodium silicate, silica fume, silicic acid, and inorganic silica gel.

5. The rapid synthesis method of low silica-to-alumina ratio ZSM-5 molecular sieve according to claim 1, characterized in that, The aluminum source is at least one of aluminum hydroxide, sodium aluminate, aluminum nitrate, and aluminum chloride.

6. The rapid synthesis method of low silica-to-alumina ratio ZSM-5 molecular sieve according to claim 1, characterized in that, The organic structure directing agent is selected from at least one of tetrapropylammonium hydroxide (TPAOH) and hexadecyltrimethylammonium bromide (CTAB).

7. The rapid synthesis method of low silica-to-alumina ratio ZSM-5 molecular sieve according to claim 1, characterized in that, The mass ratio of the nano ZSM-5 seed crystals to the silicon-aluminum mixed sol solution is 1:10-50.

8. The rapid synthesis method of low silica-to-alumina ratio ZSM-5 molecular sieve according to claim 1, characterized in that, The tubular reactor is 10-15cm long, made of stainless steel, and has high-pressure resistant seals at both ends.

9. The rapid synthesis method of low silica-to-alumina ratio ZSM-5 molecular sieve according to claim 1, characterized in that, In step (2), the stirring time is 10-30 min; in step (3), the crystallization temperature is 160℃-210℃, and the crystallization time is 10 minutes to 3 hours; in step (4), the washing is done with deionized water; the drying temperature is 80-120℃; the calcination temperature is 450-650℃, and the calcination time is 6-12 hours.

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