Preparation method of hierarchical pore zsm-5 zeolite by using tartrate as auxiliary

Abstract

The application discloses a kind of tartrate assisted synthesis multistage hole ZSM-5 molecular sieve and preparation method thereof, and relates to the technical field of molecular sieve.Preparation method includes (1) preparation of initial gel;(2) join tartrate assisted synthesis.The beneficial effect is: in the crystallization process of molecular sieve, tartrate and QAS enter the skeleton system of molecular sieve, the calcination process after crystallization end promotes the reaction of carbonate negative ion and hydrogen ion in QAS, the generation of mesoporous structure caused by released carbon dioxide simplifies the preparation process, and improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieve and its preparation method. Background Technology

[0002] ZSM-5 molecular sieve is a microporous aluminosilicate. Due to its large specific surface area, strong acidity, ordered microporous structure, good hydrothermal stability, and good shape selectivity, it plays an important role in petroleum catalytic cracking and hydrocracking. However, its inherent channel structure hinders the accessibility of macromolecular compounds to active sites, leading to reduced reactivity. Furthermore, the narrow channels impede the diffusion of reactants and products, affecting mass transfer efficiency and catalyst utilization efficiency, resulting in reduced conversion and coke deposition. These drawbacks significantly shorten the catalyst's lifespan, limiting its industrial applications.

[0003] Hierarchical porous molecular sieves with gradient channels not only possess the advantages of microporous molecular sieves but also overcome the shortcomings of narrow microporous channels. Therefore, the synthesis of hierarchical porous ZSM-5 molecular sieves has significant theoretical and practical value.

[0004] Zhao et al. (Fuel Processing Technology, 2011, 92(3):414-420) treated ZSM-5 molecular sieves with different silica-to-alumina ratios with alkali to obtain a series of hierarchical porous ZSM-5 molecular sieve products. The changes in morphology, pore structure, and catalytic activity of the products were analyzed. The study showed that silicon atoms on the high-silica ZSM-5 framework were more easily removed. Appropriate alkali treatment enhanced the mass transfer capacity of ZSM-5 molecular sieves, resulting in better selectivity and yield of light olefins in the catalytic cracking reaction of heavy oil.

[0005] Huang et al. (Angewandte Chemie International Edition, 2017, 56: 12553-12556) combined dealumination and desilication processes to construct a hierarchical porous structure (Si / Al = 10⁻²⁰) in ZSM-5 molecular sieves with high Al content. Through continuous steam and alkali treatment of ZSM-5 crystals of different particle sizes, the internal structure of the molecular sieve underwent reconstruction of silicon and aluminum atoms, leading to the removal of aluminum and the formation of mesopores. While this method of removing framework atoms has been adopted for industrial-scale production due to its ease of operation and economic benefits, its relatively low crystallinity and pore connectivity limit its further development.

[0006] Chinese patent application CN113044852A discloses a hierarchical porous ZSM-5 molecular sieve, its preparation method, and its applications. This hierarchical porous ZSM-5 molecular sieve is prepared using hemicellulose as a hard template agent. Without employing complex processes, a hierarchical porous ZSM-5 molecular sieve is synthesized, forming a variety of pore structures of different sizes. Furthermore, the different pore sizes allow for more efficient and selective adsorption of volatile organic compounds in the environment, improving the acoustic stability of sound-absorbing particles in loudspeakers.

[0007] Chinese patent application CN109368657A discloses a method for preparing a highly dispersed, hierarchical porous H-ZSM-5 molecular sieve with a framework metal, comprising the following steps: oxidative modification of carbon black to prepare hydrophilic carbon black for use as a hard template agent; preparation of nanoscale metal species using a spatially confined domain method as a metal source for framework doping; one-step in-situ hydrothermal synthesis of a metal framework-doped hierarchical porous Na-ZSM-5 molecular sieve; and preparation of H-type molecular sieves via Na-type molecular sieve ion exchange. The H-ZSM-5 molecular sieve prepared by this method retains the advantages of microporous molecular sieves while adding regular mesoporous channels to the structure, thus improving the mass transfer performance of the molecular sieve.

[0008] Serrano et al. (Chemistry of Materials, 2006, 18(10): 2462-246) devised a novel strategy to synthesize hierarchical porous ZSM-5 molecular sieves with high specific surface area, porosity, and catalytic activity: doping the original gel with the amphiphilic organosilicon surfactant phenylaminopropyltrimethoxysilane (PHAPTMS). The study showed that the hydrophilic quaternary ammonium salt group acts as a microporous structure directing agent (SDA) to guide the formation of the molecular sieve framework, while the hydrophobic siloxane group prevents the unlimited aggregation and densification of nanoparticles, thus generating mesopores. This mechanism is consistent with that of bifunctional quaternary ammonium salt template agents.

[0009] Chinese patent application CN110156043A discloses a method for preparing hierarchical porous ZSM-5 molecular sieves, comprising the following steps: adding a silicon source and a directing agent to water in a certain proportion, adding a structure directing agent, then adding ethanol, and stirring until homogeneous to obtain an initial gel. Subsequently, a silicon-aluminum source and a nitrogen-containing long-chain compound are added to the gel to synthesize a hierarchical porous ZSM-5 molecular sieve with high crystallinity, strong acidity, and good hydrothermal stability.

[0010] Chinese patent application CN106745049A discloses a method for preparing boron-modified HZSM-5 and its applications. The method involves mixing a silicon source, an aluminum source, an alkali source, and ZSM-5 molecular sieve seed crystals, followed by crystallization, washing, drying, ion exchange, and calcination to obtain boron-modified HZSM-5 molecular sieve. This method modulates the gel state using inorganic alkali metal salts, altering the crystallization and nucleation rates of the molecular sieve. Furthermore, by controlling the amount of boron added, the ratio of strong to weak acid sites is controlled. The synthesized catalyst achieves a propylene selectivity of over 44.0 wt% and a service life of over 500 hours in methanol-to-propylene reactions. This method is environmentally friendly due to the avoidance of template agent calcination, and shows great promise for application. However, the catalyst synthesized by this method has a relatively simple pore structure, limiting its further applications.

[0011] Chinese patent application CN111689505A discloses a method for synthesizing hierarchical ZSM-5 molecular sieves. This method involves modifying ZSM-5 molecular sieves with boron compounds, controlling the mass ratio of boron to the molecular sieve to create a mesoporous structure while avoiding deep damage to the sieve structure. The resulting hierarchical ZSM-5 molecular sieve exhibits high crystallinity and mesoporous specific surface area, providing a novel synthetic strategy for hierarchical ZSM-5 molecular sieves. However, this method requires separate synthesis of the molecular sieve, ion exchange, and steam treatment, making the synthesis process relatively complex.

[0012] Liu et al. (Industrial & Engineering Chemistry Research, 2022, 61(17): 6057-6064) synthesized a method that introduced boron into the ZSM-5 framework using a seed-guided method, and then removed unstable boron species from the molecular sieve by steam treatment to generate mesoporous structures. This method enabled the preparation of mesoporous ZSM-5 molecular sieves in a system of pure inorganic template agents.

[0013] While the above studies introduced mesoporous structures into microporous molecular sieve systems, the synthesis process was complex and reproducible, and the use of organic template agents caused pollution. Therefore, it is of great significance to use environmentally friendly mesoporous template agents to synthesize hierarchical porous ZSM-5 molecular sieves. Summary of the Invention

[0014] The technical problem to be solved by this invention is how to solve the problem of the complexity of the existing multi-level porous ZSM-5 molecular sieve synthesis process.

[0015] The present invention solves the above-mentioned technical problems through the following technical means:

[0016] The first aspect of this invention provides a method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves, comprising the following steps:

[0017] (1) Preparation of the initial gel:

[0018] The silicon source, aluminum source, quaternary ammonium salt (QAS) and water were mixed and stirred evenly to obtain the initial gel;

[0019] (2) Tartrate-assisted synthesis:

[0020] Tartrate was added, stirred, transferred to a polytetrafluoroethylene liner for crystallization, filtered, washed, dried, and calcined to obtain hierarchical porous ZSM-5 molecular sieve.

[0021] Beneficial effects: This invention simplifies the preparation process and improves production efficiency by crystallizing tartrate in a liquid system containing organic template agents such as QAS, followed by the reaction of carbonate anions with hydrogen ions in QAS during the subsequent calcination process, and the release of carbon dioxide leading to the formation of mesoporous structures in the molecular sieve.

[0022] Preferably, the molar ratio of quaternary ammonium salt to other components in the initial gel of step (1), based on their oxides, is: (0.01-50)Na2O:SiO2:(0.01-50)Al2O3:(0.01-50)QAS:(10-500)H2O.

[0023] Preferably, the silicon source is one or more of water glass, tetraethyl orthosilicate, and silicon powder.

[0024] Preferably, the aluminum source is one or more of aluminum sulfate, aluminum oxide, aluminum chloride, and aluminum isopropoxide.

[0025] Preferably, the quaternary ammonium salt (QAS) is one or more of tetrapropylammonium bromide (TPABr), dodecyltrimethylammonium chloride (DTAC), and dioctyldimethylammonium bromide (DDTB).

[0026] Preferably, the tartrate is added in step (2) before or after gel formation in step (1).

[0027] Preferably, the amount of tartrate added is 0.1-40% of the amount of silicon source added.

[0028] Preferably, the tartrate is one or more of sodium tartrate, potassium tartrate, and ammonium tartrate.

[0029] Preferably, the crystallization temperature is 80-200℃ and the crystallization time is 10-50h.

[0030] Preferably, the calcination conditions are a temperature of 400-600℃ and a time of 6-10h.

[0031] A second aspect of the present invention proposes a multi-level porous ZSM-5 molecular sieve prepared using the above-described preparation method.

[0032] The advantages of this invention are:

[0033] 1. This invention involves crystallizing tartrate in a liquid-phase system containing organic template agents such as QAS, followed by calcination where carbonate anions react with hydrogen ions in QAS, releasing carbon dioxide that leads to the formation of a mesoporous structure in the molecular sieve. This simplifies the preparation process and improves production efficiency.

[0034] 2. This invention uses tartrate and QAS to synthesize hierarchical ZSM-5 molecular sieves, providing a simple and easy route for the synthesis of hierarchical ZSM-5 molecular sieves. Attached Figure Description

[0035] Figure 1 This is the X-ray characteristic diffraction pattern of the hierarchical porous ZSM-5 molecular sieve obtained in Example 1 of the present invention;

[0036] Figure 2 This is the N2 adsorption-desorption curve of the multi-porous ZSM-5 molecular sieve obtained in Example 1 of the present invention. Detailed Implementation

[0037] 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 in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0039] Raw material sources: Aluminum sulfate and other raw materials are from Lanzhou Petrochemical Company of China National Petroleum Corporation, and are all industrial products; template agent is purchased from Anhui Jin'ao Chemical Co., Ltd., and is an industrial product; sodium tartrate, potassium tartrate, etc. are all commercially available reagents, industrial grade.

[0040] Analytical methods: Phase detection and confirmation were performed using a Shimadzu XRD-7000 X-ray crystal powder diffractometer. Instrument parameters: Cu-Ka rays, wavelength 0.1543 nm, tube voltage 40 kV, tube current 30 mA. Sample testing conditions: scanning angle 5-40°, scanning speed 8° / min.

[0041] The adsorption-desorption isotherms of the samples were determined using an ASAP2020M fully automated adsorption instrument manufactured by Micromeritics, USA, at liquid nitrogen temperature. Nitrogen was used as the adsorbate. The Brunauer-Emmett-Teller (BET) equation was used to calculate the specific surface area of ​​the samples based on the adsorption equilibrium isotherms between relative pressures of 0.05 and 0.25. The t-plot model was used to distinguish between the internal and external surface areas of the samples. The pore volume and pore size distribution were determined using the static volumetric method, thereby calculating the pore structure parameters.

[0042] Example 1:

[0043] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0044] (1) Preparation of the initial gel:

[0045] Water, silica powder, water glass, aluminum sulfate octahydrate and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 0.01Na2O:SiO2:0.017Al2O3:0.05TPABr:24H2O.

[0046] (2) Tartrate-assisted synthesis:

[0047] Sodium tartrate (1% of the amount of SiO2 in the silica powder and water glass in step (1)) was added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel was transferred to a polytetrafluoroethylene liner and crystallized at 170°C for 24 hours, filtered, washed, dried and calcined at 550°C for 10 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0048] Example 2:

[0049] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0050] (1) Preparation of the initial gel:

[0051] Water, silica powder, water glass, aluminum sulfate octahydrate and DTAC were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of DTAC to other components in the gel, based on their oxides, was: 50Na2O:SiO2:50Al2O3:50DTAC:500H2O.

[0052] (2) Tartrate-assisted synthesis:

[0053] Potassium tartrate (40% of the amount of SiO2 in the silica powder and water glass in step (1)) was added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel was transferred to a polytetrafluoroethylene liner and crystallized at 180°C for 20 hours, filtered, washed, dried and calcined at 400°C for 6 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0054] Example 3:

[0055] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0056] (1) Preparation of the initial gel:

[0057] Water, silica powder, water glass, aluminum chloride and DDTB were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of DDTB to other components in the gel, based on their oxides, was: 0.01Na2O:SiO2:10Al2O3:5DDTB:400H2O.

[0058] (2) Tartrate-assisted synthesis:

[0059] Sodium tartrate (2% of the amount of SiO2 in the silica powder and water glass in step (1)) was added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel was transferred to a polytetrafluoroethylene liner and crystallized at 130°C for 24 hours, filtered, washed, dried and calcined at 600°C for 7 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0060] Example 4:

[0061] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0062] (1) Preparation of the initial gel:

[0063] Water, silica powder, tetraethyl orthosilicate, aluminum sulfate octadecylhydrate and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 24Na2O:SiO2:20Al2O3:18TPABr:500H2O.

[0064] (2) Tartrate-assisted synthesis:

[0065] Ammonium tartrate (0.3% of the amount of SiO2 in silicon powder and tetraethyl orthosilicate in step (1)) was added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel was transferred to a polytetrafluoroethylene liner and crystallized at 190°C for 50 hours, filtered, washed, dried and calcined at 460°C for 8 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0066] Example 5:

[0067] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0068] (1) Preparation of the initial gel:

[0069] Water, silica powder, tetraethyl orthosilicate, aluminum sulfate octadecyl hydrate and DDTB were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of DDTB to other components in the gel, based on their oxides, was: 50Na2O:SiO2:0.02Al2O3:12DDTB:480H2O.

[0070] (2) Tartrate-assisted synthesis:

[0071] Sodium tartrate (added in an amount equal to 5% of the amount of SiO2 in the silica powder and tetraethyl orthosilicate in step (1)) was added and mixed with the initial gel and stirred at room temperature for 4 hours. The gel was then transferred to a polytetrafluoroethylene liner and crystallized at 200°C for 10 hours. After filtration, washing, drying, and calcination at 600°C for 7 hours, a hierarchical porous ZSM-5 molecular sieve was obtained.

[0072] Example 6:

[0073] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0074] (1) Preparation of the initial gel:

[0075] Water, tetraethyl orthosilicate, water glass, alumina and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 3.20Na2O:SiO2:0.20Al2O3:0.15TPABr:100H2O.

[0076] (2) Tartrate-assisted synthesis:

[0077] Ammonium tartrate (the amount added is 20% of the amount of SiO2 in water glass and tetraethyl orthosilicate in step (1)) is added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel is transferred to a polytetrafluoroethylene liner and crystallized at 170°C for 24 hours, filtered, washed, dried and calcined at 550°C for 10 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0078] Example 7:

[0079] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0080] (1) Preparation of the initial gel:

[0081] Water, water glass, aluminum isopropoxide, and DTAC were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of DTAC to other components in the gel, based on their oxides, was: 0.01Na2O:SiO2:0.01Al2O3:0.01DTAC:10H2O.

[0082] (2) Tartrate-assisted synthesis:

[0083] Ammonium tartrate (0.1% of the amount of SiO2 in the water glass) was added and mixed with the initial gel and stirred at room temperature for 4 h. The gel was then transferred to a polytetrafluoroethylene liner and crystallized at 170 °C for 23 h. After filtration, washing, drying, and calcination at 430 °C for 8 h, a hierarchical porous ZSM-5 molecular sieve was obtained.

[0084] Example 8:

[0085] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0086] (1) Preparation of the initial gel:

[0087] Water, silica powder, water glass, aluminum sulfate octadecylhydrate and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 5Na2O:SiO2:2Al2O3:2.5TPABr:200H2O.

[0088] (2) Tartrate-assisted synthesis:

[0089] Ammonium tartrate (6% of the amount of SiO2 in the silica powder and water glass in step (1)) was added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel was transferred to a polytetrafluoroethylene liner and crystallized at 170°C for 24 hours, filtered, washed, dried and calcined at 400°C for 10 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0090] Example 9:

[0091] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0092] (1) Preparation of the initial gel:

[0093] Water, silica powder, water glass, aluminum sulfate octadecylhydrate and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 5Na2O:SiO2:2Al2O3:2.5TPABr:200H2O.

[0094] (2) Tartrate-assisted synthesis:

[0095] Potassium tartrate (the amount added is 10% of the amount of SiO2 in the silica powder and water glass in step (1)) is added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel is transferred to a polytetrafluoroethylene liner and crystallized at 200°C for 50 hours, filtered, washed, dried and calcined at 400°C for 10 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0096] Example 10:

[0097] A method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves includes the following steps:

[0098] (1) Preparation of the initial gel:

[0099] Water, silica powder, water glass, aluminum sulfate octahydrate and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 5Na2O:SiO2:2Al2O3:2.5TPABr:500H2O.

[0100] (2) Tartrate-assisted synthesis:

[0101] Sodium tartrate (the amount added is 15% of the amount of SiO2 in the silica powder and water glass in step (1)) is added and mixed with the initial gel and stirred at room temperature for 4 hours; the gel is transferred to a polytetrafluoroethylene liner and crystallized at 150°C for 24 hours, filtered, washed, dried and calcined at 500°C for 9 hours to obtain hierarchical porous ZSM-5 molecular sieve.

[0102] Comparative Example 1:

[0103] (1) Preparation of the initial gel:

[0104] Water, silica powder, water glass, aluminum sulfate octahydrate and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 0.10Na2O:SiO2:0.017Al2O3:0.05TPABr:24H2O.

[0105] (2) The initial gel was stirred at room temperature for 4 hours, and then transferred to a polytetrafluoroethylene liner to crystallize at 170°C for 24 hours. After filtration, washing, drying, and calcination at 550°C for 10 hours, conventional ZSM-5 molecular sieve was obtained.

[0106] Comparative Example 2:

[0107] (1) Preparation of the initial gel:

[0108] Water, silica powder, water glass, aluminum sulfate octahydrate and TPABr were mixed and stirred at room temperature for 1 hour to prepare an initial gel, such that the molar ratio of TPABr to other components in the gel, based on their oxides, was: 0.10Na2O:SiO2:0.017Al2O3:0.05TPABr:24H2O.

[0109] (2) Add hexadecyl dimethyltrimethoxysilylpropylammonium chloride (TPHAC) at a concentration of 1% of the amount of SiO2 in the water glass. Mix with the initial gel and stir at room temperature for 4 hours. Transfer the gel to a polytetrafluoroethylene liner and crystallize at 170°C for 24 hours. After filtration, washing, drying, and calcination at 550°C for 10 hours, obtain hierarchical porous ZSM-5 molecular sieve.

[0110] The multi-level porous molecular sieves prepared in the examples were compared with the samples obtained in the comparative examples, and their pore structure parameters are listed in Table 1.

[0111] Table 1 Comparison of pore structure parameters between the examples and comparative samples

[0112] Example 1 399 277 122 0.12 Example 2 380 261 119 0.11 Example 3 376 258 118 0.10 Example 4 377 257 120 0.12 Example 5 365 249 116 0.10 Example 6 360 247 113 0.11 Example 7 321 230 91 0.08 Example 8 383 269 114 0.09 Example 9 362 260 102 0.09 Example 10 360 246 114 0.09 Comparative Example 1 313 251 62 0.08 Comparative Example 2 344 239 105 0.06

[0113] As shown in Table 1, the hierarchical porous ZSM-5 molecular sieves synthesized in Example 1 all possess abundant mesoporous specific surface areas. From the following... Figure 1 The sample exhibits characteristic diffraction peaks of ZSM-5 molecular sieve, indicating good crystallinity. Figure 2 As shown in the nitrogen adsorption-desorption diagram of the sample, the sample exhibits a distinct mesoporous structure. In summary, the synthesized hierarchical porous ZSM-5 molecular sieve possesses abundant mesoporous structure and high crystallinity.

[0114] Comparative Example 1 shows the relevant parameters of the ZSM-5 molecular sieve sample synthesized without the addition of a mesoporous template agent. As can be seen from the table, compared to Example 1, the total specific surface area and mesoporous specific surface area of ​​the synthesized sample are too low.

[0115] Comparative Example 2 shows the relevant parameters of the hierarchical ZSM-5 molecular sieve sample synthesized using TPHAC mesoporous template agent. As can be seen from the table, the total specific surface area and mesoporous specific surface area of ​​the sample synthesized using TPHAC are lower than those of Example 1, indicating that the sample results are worse.

[0116] In summary, this invention provides a method for synthesizing hierarchical porous ZSM-5 molecular sieves. During the synthesis of ZSM-5 molecular sieves, tartrate is added to a liquid-phase system containing organic template agents such as QAS for crystallization. The subsequent calcination process involves the reaction of carbonate anions with the hydrogen ions of QAS, releasing carbon dioxide which leads to the formation of a mesoporous structure in the molecular sieve. Hierarchical porous molecular sieves not only possess the advantages of microporous molecular sieves but also overcome the shortcomings of narrow pore channels. The synthesis of hierarchical porous ZSM-5 molecular sieves using this method has significant theoretical and practical value.

[0117] 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 do 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 tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves, characterized in that, Includes the following steps: (1) Preparation of the initial gel: The silicon source, aluminum source, quaternary ammonium salt and water were mixed and stirred evenly to obtain the initial gel. (2) Tartrate-assisted synthesis: Tartrate was added, stirred, transferred to a polytetrafluoroethylene liner for crystallization, filtered, washed, dried, and calcined to obtain a hierarchical porous ZSM-5 molecular sieve; the calcination conditions were a temperature of 400-600 ℃ and a time of 6-10 h.

2. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 1, characterized in that, In step (1), the molar ratio of quaternary ammonium salt to other components in the initial gel, based on their oxides, is: 0.01Na2O:SiO2:0.017Al2O3:0.05quaternary ammonium salt:24H2O.

3. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 1 or 2, characterized in that, The silicon source includes water glass; the aluminum source is one or more of aluminum sulfate octadechydrate, aluminum oxide, aluminum chloride, and aluminum isopropoxide.

4. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 3, characterized in that, The quaternary ammonium salt is one or more of tetrapropylammonium bromide, dodecyltrimethylammonium chloride, and dioctyldimethylammonium bromide.

5. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 4, characterized in that, The tartrate salt is added in step (2) before or after the gel is formed in step (1).

6. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 1, characterized in that, The tartrate is one or more of sodium tartrate, potassium tartrate, and ammonium tartrate.

7. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 1, characterized in that, The amount of tartrate added is 0.1-40% of the amount of silicon source added.

8. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 1, characterized in that, The crystallization temperature is 80-200 ℃, and the crystallization time is 10-50 h.

9. The method for tartrate-assisted synthesis of hierarchical porous ZSM-5 molecular sieves according to claim 1, characterized in that, The calcination conditions were 550 °C for 10 h.

10. The hierarchical porous ZSM-5 molecular sieve prepared by the method according to any one of claims 1-9.

Images