Method for growing zsm-5 nanosheet zeolites under fluoride-free acidic systems and applications

Abstract

The application relates to a preparation method of ZSM-5 nanosheet zeolite and belongs to the technical field of catalyst preparation. The preparation method is used for synthesizing b-axis directional growth ZSM-5 molecular sieve under a seed guiding liquid in an acid medium and a fluorine-free system. The method comprises the following steps: mixing an aluminum source, inorganic acid, inorganic alkali, a silicon source and deionized water, fully stirring to form a gel, adding a small amount of seed guiding liquid, and adjusting the pH of the synthesis gel to be between 4 and 6 by controlling the adding amount of the inorganic acid. The b-axis directional growth ZSM-5 nanosheet is obtained by crystallization treatment at a certain temperature. The method is an inorganic system synthesis in a fluorine-free system, the silicon aluminum ratio is adjustable between 30 and 120, the system is green and environmentally friendly, the cost is low, the problems of high cost, limited silicon aluminum ratio and serious environmental pollution in the fluorine-containing system and the addition of organic growth agents for synthesizing directional growth nanosheets are solved.

Description

Technical Field

[0001] This application pertains to catalysts in the petrochemical field, specifically relating to a method for preparing b-axis oriented ZSM-5 nanosheet zeolite and its application. Background Technology

[0002] ZSM-5 zeolite molecular sieves possess advantages such as tunable acidity and good hydrothermal stability, making them widely applicable in catalysis, including catalytic cracking, MTO, and MTA processes. ZSM-5 has a three-dimensional channel structure with ten-membered rings, where linear channels parallel to the b-axis intersect with sinusoidal channels parallel to the a-axis. Studies have revealed significant differences in molecular diffusion within these two types of channels. For example, small molecules like methanol and methane diffuse randomly within these intersecting channels, while larger molecules, such as short-chain hydrocarbons (C2, C3) or aromatic hydrocarbons, diffuse much faster in the b-axis channels than in the sinusoidal channels along the a-axis. Therefore, the linear channels along the b-axis are the primary diffusion channels. Reducing the length of these channels shortens the diffusion path and enhances the contact between reactant molecules and acidic sites within the channels, thereby improving the activity of the molecular sieve in acid-catalyzed reactions and effectively reducing catalyst deactivation.

[0003] Regarding the preparation of b-axis oriented MFI-type molecular sieves, researchers have proposed many methods to date. The most common methods are the additive method and the ammonium fluoride-assisted method. The additive method usually involves adding certain organic additives containing amino, imino, or hydroxyl groups, such as tributylphosphine oxide, urea, and glucose, to the synthesis system to regulate crystal growth and obtain nanosheet molecular sieves. Xiao Fengshou et al. (Chem. Commun. 2011, 47, 1048) used urea as an additive to synthesize TS-1 nanosheets, with a thickness of approximately 100-200 nm in the b-axis direction. Wei et al. (Chem. Mater. 2019, 31, 3228) used arginine as a molecular sieve growth modifier to prepare b-axis oriented silicalite-1 molecular sieves. Wang Xinping et al. (Chinese Patent Application Publication No. CN112607746A) used guanidine compounds as additives to directly synthesize b-axis oriented MFI molecular sieves with hierarchical pores. The ammonium fluoride-assisted method uses fluoride ions instead of hydroxide ions as the mineralizing agent in F... - This is a common method for synthesizing nanosheet molecular sieves in this system. Dai et al. (J.Am.Chem.Soc.2021,143,1993) obtained sheet-like S-1 and ZSM-5 molecular sieves with ammonium fluoride assistance, controlling the thickness along the b-axis to ~100 nm. However, the fluorine system is environmentally unfriendly, affecting the industrial application of this method.

[0004] Furthermore, most of the nanosheet molecular sieves currently prepared are high-silica or pure-silica MFI molecular sieves with a silica-to-alumina ratio greater than 300. This is because, during synthesis in conventional alkaline systems with the addition of growth agents, excessive Al restricts the formation of nanosheets, while during synthesis in fluorine-containing systems, the presence of fluoride ions limits the entry of Al into the molecular sieve framework. The excessively high silica-to-alumina ratio limits the application of nanosheet molecular sieves in acid-catalyzed reactions.

[0005] Therefore, finding an environmentally friendly and low-cost method for preparing ZSM-5 nanolayered zeolite is of great application value. Summary of the Invention

[0006] One objective of this application is to improve the preparation method of ZSM-5 nanosheet zeolite without using fluorine-containing substances or other additives in the preparation process.

[0007] Another objective of this application is to improve the preparation method of ZSM-5 nanosheet zeolite by introducing phosphorus element, which further improves the hydrothermal stability of ZSM-5 nanosheet zeolite.

[0008] Another objective of this application is to use the ZSM-5 nanosheet zeolite prepared in this application in an olefin catalytic cracking reaction system, thereby improving the selectivity of ethylene and propylene.

[0009] The final objective of this application is to use the ZSM-5 nanosheet zeolite prepared in this application in an olefin catalytic cracking reaction system to improve the hydrothermal stability of the catalyst in the reaction system.

[0010] A method for preparing ZSM-5 nanosheet zeolite, comprising:

[0011] (1) The aluminum source solution and the silicon source were mixed to obtain a gel.

[0012] (2) Adjust the pH of the gel to 4-6;

[0013] (3) Mix the seed crystal guiding liquid with the gel obtained in step (2), and then crystallize the mixture. After crystallization, the crystallized product is dried and calcined to obtain ZSM-5 nanosheet zeolite.

[0014] This application obtains a gel in an acidic system (such as an inorganic acid), and with the assistance of a seed-directing liquid, prepares b-axis oriented ZSM-5 nanosheets. The synthesized ZSM-5 molecular sieve has fewer lattice defects.

[0015] The ZSM-5 nanosheet zeolite prepared by the above method is used in the catalytic cracking reaction system of olefins. This ZSM-5 nanosheet zeolite exhibits excellent hydrothermal stability and can significantly improve the selectivity for ethylene and propylene. Attached Figure Description

[0016] Figure 1 The XRD patterns are of the samples obtained in Examples 1 to 3 of this invention.

[0017] Figure 2 Scanning electron microscope image of the nanosheet molecular sieve prepared in Example 1 of this invention.

[0018] Figure 3 Scanning electron microscope image of the nanosheet molecular sieve prepared in Example 2 of this invention.

[0019] Figure 4 Scanning electron microscope image of the nanosheet molecular sieve prepared in Example 3 of this invention.

[0020] Figure 5 Scanning electron microscope image of the nanosheet molecular sieve prepared in Example 6 of this invention.

[0021] Figure 6 Scanning electron microscopy of the molecular sieve sample in Comparative Example 1

[0022] Figure 7 Scanning electron microscopy of the molecular sieve sample in Comparative Example 2 Detailed Implementation

[0023] The preparation method and application of the short b-axis ZSM-5 nanosheet zeolite of the present invention are described in further detail below. This does not limit the scope of protection of this application, which is defined by the claims. Certain specific details disclosed provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented using other materials, etc., without employing one or more of these specific details.

[0024] Unless the context otherwise requires, the terms “comprising” and “including” in the specification and claims shall be understood as open-ended and inclusive, meaning “including, but not limited to”.

[0025] The terms "implementation," "an implementation," "another implementation," or "certain implementations" used in this specification refer to specific features, structures, or characteristics described in relation to the implementation, which are included in at least one implementation. Therefore, "implementation," "an implementation," "another implementation," or "certain implementations" do not necessarily all refer to the same implementation. Furthermore, specific features, structures, or characteristics can be combined in any way within one or more implementations. Each feature disclosed in this specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0026] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0027] The units in the weight-volume percentages of this invention are well known to those skilled in the art, for example, referring to the weight of the solute in 100 ml of solution.

[0028] In this invention, the concentration unit "M" of the solution represents mol / L.

[0029] The term "roasting" refers to the process of treating a substance at high temperatures in an air atmosphere.

[0030] In this application, the amount of silicon source used is calculated as SiO2, and the amount of aluminum source used is calculated as Al2O3.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0032] A method for preparing short b-axis ZSM-5 nanosheet zeolite includes:

[0033] (1) The aluminum source solution and the silicon source were mixed to obtain a gel.

[0034] (2) Adjust the pH of the gel to 4-6;

[0035] (3) Mix the seed crystal guiding liquid with the gel obtained in step (2), and then crystallize the mixture. After crystallization, the crystallized product is dried and calcined to obtain ZSM-5 nanosheet zeolite.

[0036] In some implementations, an inorganic acid is used in step (2) to adjust the pH of the gel.

[0037] The inorganic acid mentioned includes one or a mixture of several of sulfuric acid, phosphoric acid, and nitric acid.

[0038] Alternatively, in step (2), the pH of the gel can be adjusted using phosphoric acid.

[0039] In the process of synthesizing ZSM-5 nanosheet zeolite, under fluorine-free conditions, the growth rate of different crystal planes can be effectively controlled by adjusting the pH of the synthesis gel to 4-6 with inorganic acid, thereby adjusting the length and thickness of the nanosheets and preparing b-axis oriented ZSM-5 nanosheets. The thickness of the b-axis wafers can be controlled within 80-150 nm.

[0040] In some embodiments, the phosphorus (P) content in ZSM-5 nanosheet zeolite is approximately 0.4 wt% to 2.0 wt%. The P content is expressed as the highest valence oxide.

[0041] Alternatively, the phosphorus (P) content in ZSM-5 nanosheet zeolite may be approximately 0.5 wt%–1.5 wt%. The P content is expressed as the highest valence oxide.

[0042] Alternatively, in ZSM-5 nanosheet zeolite, the phosphorus (P) content is approximately 1.2 wt%. The P content is expressed as the highest valence oxide.

[0043] In the preparation process, phosphoric acid is used to adjust the pH of the gel. On the one hand, this adjusts the gel to acidic conditions for crystallization, resulting in short b-axis nanosheet structures with specific morphologies. On the other hand, the introduction of heteroatoms P into ZSM-5 leads to improved catalytic performance of the resulting molecular sieve in olefin catalysis systems. In particular, controlling the P content within the range of 0.4 wt%–2.0 wt% significantly improves hydrothermal stability.

[0044] During the process of adjusting the pH of the gel, an alkaline source can be added as appropriate according to the actual required pH value. The alkaline source can be one or more of sodium hydroxide and potassium hydroxide, with sodium hydroxide being more preferred.

[0045] In some embodiments, the amount of seed crystal guiding liquid added in step (3) is 5 wt% to 10 wt% of the gel mass.

[0046] In some implementations, the molar ratio of silicon source to aluminum source is 100:(0.8 to 3).

[0047] An optional scheme is a silicon source to aluminum source molar ratio of 100:(0.9~2).

[0048] The molar ratio of silicon source to water is 100:(1800~4000).

[0049] The ZSM-5 nanosheet molecular sieve prepared in this application has a medium to low silicon-to-aluminum ratio range, and the silicon-to-aluminum oxide ratio (SiO2 / Al2O3) can be adjusted between 30 and 120. The preparation method is to synthesize in an almost completely inorganic acidic system, and the synthesized molecular sieve has fewer lattice defects.

[0050] In some implementations, the temperature during the crystallization process in step (3) is in the range of 150 to 180°C.

[0051] Crystallization time: 24h to 48h.

[0052] Alternatively, the crystallization temperature is approximately 160°C.

[0053] The roasting temperature is 550-650℃. The roasting time is 2-8 hours.

[0054] The ZSM-5 obtained in this application can be crystallized under acidic conditions (pH = 4-6, especially phosphoric acid) to synthesize b-axis oriented ZSM-5 nanosheets. The acidic conditions also avoid excessive dissolution and loss of silicon source, and the yield of solid product is as high as 95% or more.

[0055] The drying temperature should be controlled between 80-120℃. It is sufficient to keep the water content of the solid within a certain range.

[0056] Seed guiding liquid can be prepared using methods disclosed in existing technologies, or commercially available products can be purchased directly.

[0057] Alternatively, the seed guiding liquid of this application is prepared by the following method: organosilicon, template agent and water are mixed to form a solution, and the resulting solution is crystallized to obtain the seed guiding liquid.

[0058] Organosilicones include alkyl silicates, such as tetraethyl silicate or tetramethyl silicate.

[0059] The molar ratio of organosilicon to template agent is 1:(0.1~0.15).

[0060] The molar ratio of organosilicon to H2O is 1:(15-20).

[0061] The amount of organosilicon used is measured in SiO2.

[0062] In some embodiments, the template agent for synthesizing the seed crystal guiding liquid is one of tetrapropylammonium hydroxide and tetrapropylammonium bromide. Preferably, the template agent is tetrapropylammonium hydroxide.

[0063] In some embodiments, during the preparation of the seed crystal guiding liquid, the solution is crystallized at a temperature of 70–90°C.

[0064] Crystallization time: 12h to 24h.

[0065] Alternatively, the crystallization temperature is approximately 90°C.

[0066] An alternative approach is to stir and mix the solution at 15-40℃ for 12-30 hours before crystallization.

[0067] In this application, the aluminum source and silicon source can be any of the raw materials commonly used in the prior art for preparing molecular sieves.

[0068] For example, the aluminum source may be one or a combination of two or more of aluminum isopropoxide, boehmite, sodium aluminate, and aluminum sulfate.

[0069] The silicon source may be one or a combination of two or more of silica sol, water glass, silica, and tetraethyl orthosilicate.

[0070] The ZSM-5 molecular sieve prepared by the above method has a short b-axis nanosheet structure, and the thickness of the b-axis wafers can be controlled within 80-150 nm. This molecular sieve exhibits excellent catalytic performance in olefin catalytic cracking reaction systems, with high selectivity for small molecule olefins and a long service life.

[0071] On the other hand, the ZSM-5 nanosheet zeolite prepared in this application is used in the catalytic cracking reaction system of olefins.

[0072] Under the action of the ZSM-5 nanosheet zeolite obtained by the above preparation method, olefins undergo a cracking reaction at a reaction temperature of 500-550℃.

[0073] Preferably, the reaction pressure is about 1 atm (one standard atmosphere).

[0074] More preferably, the mass hourly space velocity is approximately 6 h. -1 -10·h -1 .

[0075] Olefins and steam are co-fed, with a water-to-oil mass ratio of 0.6.

[0076] The olefins include monoolefins, preferably C4-C8 monoolefins, such as pentene, hexene, heptene, and octene. C4-C8 olefins are often byproducts of many processes, making their use as raw materials for catalytic cracking more practically significant.

[0077] The ZSM-5 nanosheet zeolite prepared in this application can significantly improve the combined selectivity of ethylene and propylene in the catalytic cracking of olefins, and has a long service life.

[0078] The ZSM-5 nanosheet zeolite of the present invention and its catalytic effect are further illustrated below with specific embodiments. All substances used in the following embodiments are chemically pure standards.

[0079] Example 1

[0080] Preparation of ZSM-5 molecular sieve seed crystal guiding liquid: Weigh 8.12g of TPAOH (25%) solution, add 20g of ethyl silicate dropwise while stirring, stir at room temperature for 24h, and then put it into a polytetrafluoroethylene-lined reactor. Crystallize at 90℃ for 24h. After the reaction is completed, cool it rapidly. The seed crystal guiding liquid can be stored directly in a cool place for later use without any treatment.

[0081] Preparation of ZSM-5 nanosheet zeolite:

[0082] Weigh 1.2g of aluminum sulfate octadechydrate, 6.1g of phosphoric acid, and 18g of deionized water, mix and stir until completely dissolved. Add 25g of water glass (containing 30% SiO2 and 9% Na2O) and 10g of deionized water, stir until homogeneous to form a gel. Add 0.8g of seed crystal guiding liquid to the gel and continue stirring for 2 hours, maintaining the gel pH at approximately 5. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and calcine it in a muffle furnace at 550℃ for 2 hours to obtain b-axis oriented P-ZSM-5 nanosheet zeolite. The product yield is approximately 98.5%.

[0083] Example 2

[0084] The preparation of the ZSM-5 molecular sieve seed guiding liquid is the same as in Example 1.

[0085] Preparation of ZSM-5 nanosheet zeolite:

[0086] Weigh 1.2g of aluminum sulfate octadechydrate, 4.5g of phosphoric acid, and 18g of deionized water, mix and stir until completely dissolved. Add 25g of water glass (containing 30% SiO2 and 9% Na2O) and 10g of deionized water, and stir until homogeneous to form a gel. Add 0.8g of seed crystal guiding liquid to the gel and continue stirring for 1 hour, maintaining the gel pH at approximately 6. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and calcine it in a muffle furnace at 550℃ for 2 hours to obtain b-axis oriented P-ZSM-5 nanosheet zeolite with a yield of approximately 96.3%.

[0087] Example 3

[0088] The preparation of the ZSM-5 molecular sieve seed guiding liquid is the same as in Example 1.

[0089] Preparation of ZSM-5 nanosheet zeolite:

[0090] Weigh 1.2g of aluminum sulfate octadechydrate, 3.5g of phosphoric acid, and 18g of deionized water, mix and stir until completely dissolved. Add 25g of water glass (containing 30% SiO2 and 9% Na2O) and 10g of deionized water, and stir until homogeneous to form a gel. Add 0.8g of seed crystal guiding liquid to the gel and continue stirring for 2 hours, maintaining the gel pH at approximately 7. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and calcine it in a muffle furnace at 550℃ for 2 hours to obtain b-axis oriented P-ZSM-5 nanosheet zeolite with a yield of approximately 95.2%.

[0091] Example 4

[0092] The preparation of the ZSM-5 molecular sieve seed guiding liquid is the same as in Example 1.

[0093] Preparation of ZSM-5 nanosheet zeolite:

[0094] Weigh 1.2g of aluminum sulfate octadechydrate, 2.8g of sulfuric acid, and 18g of deionized water, mix and stir until completely dissolved. Add 25g of water glass (containing 30% SiO2 and 9% Na2O) and 10g of deionized water, and stir until homogeneous to form a gel. Add 0.8g of seed crystal guiding liquid to the gel and continue stirring for 2 hours, maintaining the gel pH at approximately 7. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and calcine it in a muffle furnace at 550℃ for 2 hours to obtain b-axis oriented ZSM-5 nanosheet zeolite with a yield of approximately 95.5%.

[0095] Example 5

[0096] The preparation of the ZSM-5 molecular sieve seed guiding liquid is the same as in Example 1.

[0097] Preparation of ZSM-5 nanosheet zeolite:

[0098] Weigh 2.4g of aluminum sulfate octadechydrate, 3.5g of phosphoric acid, and 18g of deionized water, mix and stir until completely dissolved. Add 25g of water glass (containing 30% SiO2 and 9% Na2O) and 10g of deionized water, and stir until homogeneous to form a gel. Add 0.8g of seed crystal guiding liquid to the gel and continue stirring for 2 hours, maintaining the gel pH at approximately 6. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and calcine it in a muffle furnace at 550℃ for 2 hours to obtain b-axis oriented P-ZSM-5 nanosheet zeolite with a yield of approximately 93.5%.

[0099] Example 6

[0100] The preparation of the ZSM-5 molecular sieve seed guiding liquid is the same as in Example 1.

[0101] Preparation of ZSM-5 nanosheet zeolite:

[0102] Weigh 0.8g of aluminum sulfate octadechydrate, 8.2g of phosphoric acid, and 18g of deionized water, mix and stir until completely dissolved. Add 25g of water glass (containing 30% SiO2 and 9% Na2O) and 10g of deionized water, and stir until homogeneous to form a gel. Add 0.8g of seed crystal guiding liquid to the gel and continue stirring for 2 hours, maintaining the gel pH at approximately 6. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and calcine it in a muffle furnace at 550℃ for 2 hours to obtain b-axis oriented P-ZSM-5 nanosheet zeolite with a yield of approximately 97.4%.

[0103] Example 7

[0104] The preparation of the ZSM-5 molecular sieve seed guiding liquid is the same as in Example 1.

[0105] Preparation of ZSM-5 nanosheet zeolite:

[0106] Weigh 0.85g sodium aluminate, 5.2g phosphoric acid, and 15g deionized water, mix and stir until completely dissolved. Dissolve 2.4g sodium hydroxide in 10g water, stirring until completely dissolved to form a clear liquid. Add the sodium hydroxide solution dropwise to the aluminum solution, stir, and then add 30g silica sol (40%) to form a gel. Add 0.8g seed crystal guiding liquid to the gel and continue stirring for 2 hours, maintaining the gel pH at approximately 5. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and then calcine it in a muffle furnace at 550℃ for 2 hours to obtain b-axis oriented P-ZSM-5 nanosheet zeolite with a yield of approximately 98.1%.

[0107] Comparative Example 1

[0108] The preparation of the ZSM-5 molecular sieve seed guiding liquid is the same as in Example 1.

[0109] Preparation of ZSM-5 nanosheet zeolite:

[0110] Weigh 1.2g of aluminum sulfate octadechydrate, 1.0g of sulfuric acid, and 18g of deionized water, mix and stir until completely dissolved. Add 25g of water glass (containing 30% SiO2 and 9% Na2O) and 10g of deionized water, and stir until homogeneous to form a gel. Add 0.8g of seed crystal guiding liquid to the gel and continue stirring for 2 hours, maintaining the gel pH at approximately 10. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 160℃ for 25 hours. After crystallization, wash the resulting solid product, dry it at 100℃, and calcine it in a muffle furnace at 550℃ for 2 hours to obtain hexagonal ZSM-5 crystals. The solid yield is approximately 81%. The catalytic evaluation results are shown in Table 2.

[0111] Comparative Example 2

[0112] Weigh 0.78g of sodium aluminate and 15g of deionized water, mix and stir until completely dissolved. Dissolve 2.4g of sodium hydroxide in 10g of water, stirring until completely dissolved to form a clear liquid. Add the sodium hydroxide solution dropwise to the aluminum solution, stir, and then add 30g of silica sol (40%) to form a gel. Add 0.8g of seed crystal powder to the gel, continue stirring for 2 hours, the gel pH is 11, and crystallize at 160℃ for 25 hours. After the reaction is complete, wash the obtained solid product after crystallization, dry at 100℃, and calcine the dried solid product in a muffle furnace at 550℃ for 2 hours to obtain coffin-shaped large-grained ZSM-5 crystals. The product yield is approximately 79.2%. The catalytic evaluation results are shown in Table 2.

[0113] Comparative Example 3

[0114] Weigh 0.05 g of sodium aluminate and 58 g of deionized water, mix and stir until completely dissolved. Add 32.5 g of tetrapropylammonium hydroxide (25%) solution dropwise to the aluminum solution and stir. Then add 21 g of ethyl silicate to form a gel. Add 0.3 g of urea to the gel and continue stirring for 1-2 hours. Crystallize at 180 °C for 4 days. After the reaction is complete, wash the obtained solid product after crystallization and dry it at 100 °C. Place the dried solid product in a muffle furnace and calcine at 550 °C for 6 hours to obtain nanosheet molecular sieve samples. The product yield is approximately 82.2%. The catalytic evaluation results are shown in Table 2.

[0115] Experimental Example 1

[0116] This experiment analyzed the ZSM-5 molecular sieves prepared in Examples 1-6 and Comparative Examples 1-3 using X-ray fluorescence spectroscopy (XRF). The results are shown in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] Experiment Example 2

[0121] This experimental example analyzes the XRD diffraction patterns of the ZSM-5 nanosheet zeolites prepared in Examples 1-3, such as... Figure 1 As shown in the figure. The results show that the ZSM-5 nanosheet zeolites in Examples 1-3 all have obvious ZSM-5 characteristic peaks. At the same time, no impurity crystal phase diffraction peaks were observed, indicating that pure phase ZSM-5 molecular sieves can be obtained under acidic media with good crystallinity.

[0122] Experimental Example 3

[0123] This experiment analyzed the ZSM-5 zeolites prepared in Examples 1-3, 6, and Comparative Examples 1-2 using scanning electron microscopy (SEM). The results are shown in the appendix. Figure 2-7 As shown.

[0124] Figure 2 , 3 Figures 4 and 5 show SEM images of samples from Examples 1-3. As can be seen from the figures, the morphology of the samples synthesized in the acidic medium is that of nanosheets grown along the b-axis, with a thickness of 85-135 nm along the b-axis. As the pH of the synthesis medium increases from 5 to 7, the thickness along the b-axis does not change significantly, while the crystal size along the c-axis gradually decreases. That is, as the pH of the synthesis medium increases, the trend of directional growth weakens, and the thickness difference between the c-axis and b-axis gradually decreases, with the size decreasing from 1.8 μm to approximately 850 nm.

[0125] Figure 5The image shows the SEM image of the sample from Example 6. As can be seen from the image, changing the silicon-to-aluminum ratio in the synthesis system does not change the crystal morphology of the sample, which is still a b-axis oriented growth of nanosheets.

[0126] Figure 6 The image shows the SEM image of sample 1 (Comparative Example). As can be seen from the image, the ZSM-5 sample synthesized by the seed-directed liquid method under alkaline conditions showed no directional growth trend and had a hexagonal structure.

[0127] Figure 7 The image shows the SEM image of sample 2 (Comparative Example). As can be seen from the image, the ZSM-5 sample synthesized by the seed method under alkaline conditions is a typical coffin-shaped crystal with a grain size of approximately 2.5 μm.

[0128] Experiment Example 4

[0129] This experiment tested the catalytic performance of the ZSM-5 nanolayered zeolites prepared in Examples 1-4, 6 and Comparative Examples 1-3.

[0130] The obtained sample was pressed into tablets and ground to a fineness of 40–80 mesh. 1.0 g of sample was weighed and loaded into a fixed-bed reactor for olefin catalytic cracking reaction evaluation. 1-Hexene was used as the feedstock, the reaction temperature was 550 °C, steam was co-fed, the water-to-oil mass ratio (mass of steam to olefins) was 0.6, and the space velocity was 6 h⁻¹. -1 The evaluation results are shown in Table 2.

[0131] Table 2

[0132]

[0133]

[0134] The conversion rates of Examples 1-4, 6 and Comparative Examples 1-3 of this application are above 95%. The catalyst lifetime in Table 2 refers to the time during which the 1-hexene conversion is maintained above 95%.

Claims

1. An application of ZSM-5 nanosheet zeolite in an olefin catalytic cracking reaction system, comprising: In the olefin cracking reaction, the reaction temperature is 500-550℃, and the olefin is a C4-C8 monoolefin; The preparation method of the ZSM-5 nanosheet zeolite includes: (1) The aluminum source solution and the silicon source are mixed to obtain a gel. (2) Use phosphoric acid to adjust the pH of the gel to 4-6; (3) The seed crystal guiding liquid is mixed with the gel obtained in step (2), and then crystallized. After crystallization, the crystallized product is dried and calcined to obtain short b-axis ZSM-5 nanosheet zeolite; In ZSM-5 nanosheet zeolite, the content of P is 0.4wt%-2.0wt%, and the content of P is calculated as the highest valence oxide. The amount of seed crystal guiding liquid added is 5wt% to 10wt% of the gel mass; The preparation method of the seed crystal guiding liquid includes: mixing organosilicon, template agent and water to form a solution, and then crystallizing the resulting solution at a temperature of 70~90℃ to obtain the seed crystal guiding liquid. The molar ratio of organosilicon to template agent is 1:(0.1 ~ 0.15), and the molar ratio of organosilicon to H2O is 1:(15 ~ 20).

2. The application according to claim 1, characterized in that, In ZSM-5 nanosheet zeolite, the content of P is 0.5wt%-1.5wt%.

3. The application according to claim 1, characterized in that, The content of P in ZSM-5 nanosheet zeolite is 1.2 wt%.

4. The application according to any one of claims 1-3, characterized in that, The molar ratio of silicon source to aluminum source is 100:(0.8~3).

5. The application according to any one of claims 1-3, characterized in that, The molar ratio of silicon source to aluminum source is 100:(0.9~2).

6. The application according to claim 4, characterized in that, The molar ratio of silicon source to water is 100:(1800~4000).

7. The application according to any one of claims 1-3, characterized in that, During the preparation of the seed crystal guiding liquid, the crystallization temperature is 90℃.

8. The application according to any one of claims 1-3, characterized in that, In step (3), the temperature during the crystallization process is in the range of 150 ~ 180℃.

9. The application according to claim 8, characterized in that, In step (3), the crystallization time is 24h ~ 48h.

10. The application according to any one of claims 1-3, characterized in that, The roasting temperature is 550-650℃.

11. The application according to claim 10, characterized in that, The roasting time is 2-8 hours.

12. The application according to claim 1, characterized in that, In the olefin cracking reaction, the reaction pressure is 1 atm.

13. The application according to claim 1, characterized in that, In the cracking reaction of olefins, the mass hourly space velocity is 6-10 h⁻¹. -1 .

14. The application according to claim 1, characterized in that, In the olefin cracking reaction, olefins and steam are co-fed, with a water-to-oil mass ratio of 0.6.

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