A preparation method of hierarchical macroporous-microporous ZSM-5 molecular sieve and its product

Abstract

The invention discloses a preparation method of a hierarchical pore macroporous-microporous ZSM-5 molecular sieve, comprising the following steps: (1) tetrapropylammonium hydroxide, sodium metaaluminate, sodium hydroxide, deionized water and anhydrous ethanol are uniformly mixed to obtain a silicon source treatment solution; silicon oxide microspheres are placed in the silicon source treatment solution as a silicon source for ultrasonic dispersion, and then dried at 40-60°C to obtain a xerogel; (2) the xerogel is subjected to steam-assisted crystallization to obtain a solid product, which is then calcined to obtain a sodium-type hierarchical pore macroporous-microporous ZSM-5 molecular sieve, which can be ammonium exchanged and converted into a hydrogen-type hierarchical pore macroporous-microporous ZSM-5 molecular sieve catalyst. The present invention uses low-cost, large-scale synthesizable silicon oxide microspheres as self-templates, realizes the construction of a hierarchical pore macroporous-microporous structure in a ZSM-5 molecular sieve system, and effectively improves the diffusion and circulation of the molecular sieve.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve synthesis, and in particular relates to a preparation method of hierarchical macroporous-microporous ZSM-5 molecular sieve and its product. Background Art

[0002] Zeolite molecular sieves are a type of inorganic microporous crystalline material with high specific surface area, regular pore structure, strong acidity, good thermal and hydrothermal stability, etc. They are widely used in petrochemical, fine chemical and daily chemical fields. However, in actual applications, the narrow micropore structure (<2nm) of the molecular sieve severely limits the flow and diffusion of guest molecules, greatly reducing its catalytic activity. Introducing a pore structure with a larger pore size into the molecular sieve can effectively shorten the micropore diffusion distance, thereby improving the flow and diffusion of the microporous molecular sieve material. Hierarchical pore molecular sieves, which combine the high flow and diffusion of the macroporous-mesoporous structure and the high catalytic selectivity of the microporous structure, are an effective way to solve the bottleneck of their catalytic applications. Therefore, in recent years, the research on hierarchical pore molecular sieve materials has rapidly become a hot topic in the research field of new molecular sieve catalytic materials.

[0003] In recent years, researchers both domestically and internationally have made significant progress in the design and synthesis of hierarchical pore size molecular sieves. In industry, desiliconization or dealumination post-treatment methods are commonly used to introduce mesoporous channels within molecular sieve crystals. While these post-treatment methods are simple to operate, the resulting mesoporous / macroporous channel structure is uncontrollable and can easily damage the molecular sieve framework, severely affecting its acidity and crystallinity. Using hard or soft templates to construct mesoporous or macroporous structures within molecular sieve materials is the most direct and effective approach to preparing hierarchical pore size molecular sieves. Jacobsen et al. used carbon nanoparticles as mesoporous templates to prepare mesoporous ZSM-5 zeolites with intracrystalline pore structures (J. Am. Chem. Soc., 2000, 122, 7116-7117); Professor Xiao Fengshou's team used cationic polymers as mesoporous templates to prepare mesoporous Beta zeolites (J. Am. Chem. Soc., 2014, 136, 2503-2510); and Academician Xie Zaiku's team used copolymer templates as mesoporous templates to prepare mesoporous ZSM-5 zeolites (Chinese J. Catal., 2013, 34, 1429-1433). However, these traditional template methods all require template removal, which is complex and time-consuming, making them unsuitable for industrial applications.

[0004] Compared to traditional template methods, the template material in the self-templated method not only serves as a supporting framework for the traditional template but can also be converted into a precursor and directly participate in the formation of the hierarchical structure. Therefore, the self-templated method offers significant advantages in the structural design and component optimization of hierarchical molecular sieves, thanks to its reduced reaction steps and the absence of an additional template. Professor Schwieger's research group used mesoporous silica as a self-template and silicon source to produce hierarchical MFI molecular sieves with intracrystalline macroporous structures through a dissolution-recrystallization process under steam-assisted crystallization conditions (Adv Mater, 2015, 27, 1066-1070). This is because the presence of mesopores allows the alkaline source, tetrapropylammonium hydroxide, to partially enter the silica particles and easily encapsulate them, promoting the dissolution process during the crystallization reaction. Furthermore, the rich mesoporous structure reduces the particle density, facilitating the particle sedimentation and drying process during xerogel preparation. However, the above method is difficult to be industrialized on a larger scale. The main reason is that the synthesis methods of mesoporous silica microspheres reported so far are relatively complex, resulting in a wide particle size distribution and the inability to fully control the particle size. This makes it difficult to achieve large-scale synthesis of monodisperse mesoporous silica. Therefore, the development of a simple, low-cost, and large-scale method for preparing hierarchical pore size molecular sieves based on a self-templating method is of great significance for promoting their industrial application. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of existing hierarchical pore molecular sieve preparation technology, such as high synthesis cost, complex synthesis process, and difficulty in large-scale synthesis. Low-cost, large-scale synthesizable silica microspheres are used as self-templates to achieve the preparation of hierarchical pore macroporous-microporous ZSM-5 molecular sieve materials. The synthesis process is simple, efficient, green and environmentally friendly, and is expected to be used for large-scale production.

[0006] The technical solution of the present invention can be achieved through the following technical measures:

[0007] A method for preparing hierarchical macroporous-microporous ZSM-5 molecular sieve comprises the following steps:

[0008] (1) Tetrapropylammonium hydroxide, sodium metaaluminate, sodium hydroxide, deionized water, and anhydrous ethanol are uniformly mixed to obtain a silicon source treatment solution; silicon oxide microspheres are placed in the silicon source treatment solution as a silicon source, ultrasonically dispersed, and then dried at 40-60° C. to obtain a xerogel;

[0009] (2) The dry gel is subjected to steam-assisted crystallization to obtain a solid product, which is then calcined to obtain a sodium-type hierarchical pore macroporous-microporous ZSM-5 molecular sieve.

[0010] According to the above scheme, the sodium-type hierarchical macroporous-microporous ZSM-5 molecular sieve can be ammonium exchanged and calcined to convert it into a hydrogen-type hierarchical macroporous-microporous ZSM-5 molecular sieve, which can also be called a hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst. The specific process of ammonium exchange and calcination is as follows: the sodium-type hierarchical macroporous-microporous ZSM-5 molecular sieve is placed in a 1M ammonium nitrate solution, stirred at 80°C for 3 hours, repeated three times, and then calcined at a temperature of 500-600°C for 5-7 hours.

[0011] According to the above scheme, in step (1), the molar ratio of silicon oxide, tetrapropylammonium hydroxide, sodium aluminate, and sodium hydroxide is 1:(0.06-0.15):(0-0.05):(0.03-0.10); the mass ratio of the total mass of tetrapropylammonium hydroxide, sodium aluminate, and sodium hydroxide to water is 1:(2.5-25); and the mass ratio of ethanol to silicon oxide microspheres is 1-5.

[0012] Furthermore, in step (1), the silicon source treatment solution can also be prepared by mixing tetrapropylammonium hydroxide aqueous solution, sodium metaaluminate aqueous solution, sodium hydroxide aqueous solution and anhydrous ethanol. In step (1), the mass fraction of the tetrapropylammonium hydroxide aqueous solution is 35-45 wt.%, with a mass of 0.3-7 g; the mass fraction of the sodium metaaluminate aqueous solution is 1-3 wt.%, with a mass of 0.3-17 g; the mass fraction of the sodium hydroxide aqueous solution is 3-5 wt.%, with a mass of 0.25-5 g; the mass of anhydrous ethanol is 0.5-5 g; and the mass of the silicon source is 0.5-5 g. In this step, the solutes in each solution can be configured with different mass fractions, but the mass ratio of water to solute (solute refers to tetrapropylammonium hydroxide, sodium metaaluminate, and sodium hydroxide) in the silicon source treatment solution must be maintained between 2.5 and 25 under the premise that the solutes are completely dispersed.

[0013] According to the above scheme, in step (1), the silicon source is silicon oxide microspheres with a particle size of 300 to 600 nm.

[0014] According to the above scheme, in step (1), the ultrasonic time is 0.5 to 1 h, and the ultrasonic power is 50 to 70 W.

[0015] According to the above scheme, in step (1), the drying time is 6 to 24 hours.

[0016] According to the above scheme, in step (2), the crystallization temperature is 150-180° C., and the crystallization time is 24-72 h.

[0017] According to the above scheme, in step (2), the calcination temperature is 500-600°C and the calcination time is 5-7h.

[0018] The present invention uses silica microspheres as a silicon source and macroporous self-template, and tetrapropylammonium hydroxide as a microporous template. During steam-assisted crystallization, a macroporous structure is generated in situ through a "dissolution-recrystallization" process to prepare a hierarchical macroporous-microporous ZSM-5 molecular sieve. The hierarchical macroporous-microporous ZSM-5 molecular sieve prepared by the present invention has a relatively uniform grain size, with a particle size distribution of 1 to 3 μm, and micropores with a pore size mainly concentrated around 0.4 to 0.6 nm. The grains have a rich macroporous structure, with interconnected macropores within the grains, and pore diameters mainly distributed between 300 and 500 nm.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention uses low-cost, large-scale synthesizable silica microspheres as self-templates to achieve the construction of hierarchical pore macroporous-microporous structures in the ZSM-5 molecular sieve system, effectively improving the diffusion and fluidity of the molecular sieve. In particular, in the preparation process of the dry gel, the present invention adds measures such as ultrasonic treatment, addition of ethanol additives, and addition of a second alkali source, sodium hydroxide, to achieve the macroporous template effect of the silica microspheres. Among them, ultrasonic treatment and ethanol additives help the silica microspheres to be fully dispersed in the silicon source treatment solution and then settle and densely accumulate during the drying process, so that the remaining components are evenly distributed in the gaps formed by the accumulation of silica microspheres; and the addition of a second alkali source, sodium hydroxide, which is more corrosive to silica, can enhance the silica dissolution process in the crystallization reaction, making up for the problem of weakened dissolution process after the loss of mesopores, thereby finally achieving the use of low-cost, large-scale synthesizable silica microspheres to prepare hierarchical pore macroporous-microporous ZSM-5 molecular sieve materials with adjustable silicon-aluminum ratio.

[0021] (2) The present invention uses silica microspheres as a silicon source, which has low synthesis cost and can be synthesized in large quantities. At the same time, the self-template synthesis process is simple and green and environmentally friendly, so it can be used for large-scale synthesis of hierarchical pore molecular sieves. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope image of the silicon oxide microspheres used in the embodiments of the present invention;

[0023] Figure 2 This is an X-ray diffraction pattern of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention;

[0024] Figure 3 This is a scanning electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention;

[0025] Figure 4 This is a transmission electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention;

[0026] Figure 5 N2 adsorption-desorption curve (a) and micropore size distribution diagram (b) of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention;

[0027] Figure 6 This is a scanning electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 2 of the present invention;

[0028] Figure 7 This is a scanning electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 3 of the present invention;

[0029] Figure 8 This is a scanning electron microscope image of the sodium molecular sieve prepared in Comparative Example 1 of the present invention;

[0030] Figure 9 This is a scanning electron microscope image of the sodium molecular sieve prepared in Comparative Example 2 of the present invention;

[0031] Figure 10 This is a scanning electron microscope image of the sodium molecular sieve prepared in Comparative Example 3 of the present invention;

[0032] Figure 11 This is a scanning electron microscope image of the micron-sized molecular sieve catalyst prepared in Comparative Example 4 of the present invention;

[0033] Figure 12 These are the catalytic performance evaluation results of the ZSM-5 molecular sieve catalysts prepared in Comparative Example 4 and Example 2 of the present invention, (a) is Comparative Example 4, and (b) is Example 2. DETAILED DESCRIPTION

[0034] In order to better understand the present invention, the content of the present invention is further explained below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0035] In the following examples, unless otherwise specified, all reagents described are commercially available chemically pure chemical reagents.

[0036] In the following examples, the silicon dioxide particles (also called silicon dioxide microspheres) used are spherical in shape and have a relatively uniform particle size, which is basically in the range of 500 to 650 nm. Figure 1 shown.

[0037] Example 1

[0038] A method for preparing a hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst comprises the following steps:

[0039] (1) 0.638 g of 40 wt.% TPAOH solution, 0.68 g of 2 wt.% NaAlO2 solution, 0.418 g of 4 wt.% NaOH solution and 0.5 g of anhydrous ethanol were added in sequence into a crucible containing 0.5 g of silica microspheres (the molar ratio of silica, tetrapropylammonium hydroxide, sodium aluminate and sodium hydroxide was 1:0.15:0.02:0.05; the mass ratio of the total mass of tetrapropylammonium hydroxide, sodium aluminate and sodium hydroxide to water was about 1:5). After ultrasonication for 60 min, the mixture was dried at 40 °C for 6 h, and then the temperature was raised to 60 °C and dried for more than 2 h until the reaction precursor solution was completely dried to obtain a dry gel.

[0040] (2) The xerogel was placed in a 150 ml reactor containing 6 g of deionized water and crystallized at 180°C with steam assistance for 24 h. The solid product was removed, centrifuged, washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6 h.

[0041] (3) The sample obtained in step (2) was placed in a 1M ammonium nitrate solution (solid-liquid ratio 1g:25ml) for ammonium exchange, stirred at 80°C for 3h, repeated three times, and then calcined at 550°C for 6h to obtain a hierarchical pore macroporous-microporous ZSM-5 molecular sieve catalyst.

[0042] Figure 2 This is the X-ray diffraction pattern of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention. The results show that the sample has typical diffraction peaks of ZSM-5 molecular sieve with high peak intensity, indicating that the sample is a ZSM-5 molecular sieve material with good crystallinity;

[0043] Figure 3 This is a scanning electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention. The results show that the sample has a relatively uniform grain size, with a particle size distribution of 1 to 2 μm, and the grains have a rich macroporous structure.

[0044] Figure 4 This is a transmission electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention. The results show that the macroporous structure inside the grains is interconnected, and the pore diameter is mainly distributed in the range of 300-500 nm.

[0045] Figure 5 (a) N2 adsorption-desorption curve and (b) micropore size distribution of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 1 of the present invention. The results show that the synthesized hierarchical pore ZSM-5 molecular sieve material has a rich microporous structure and a BET specific surface area of ​​422 m 2 / g, the pore diameter of micropores is mainly concentrated in the range of 0.4-0.6nm, about 0.5nm.

[0046] Example 2

[0047] A method for preparing a hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst comprises the following steps:

[0048] (1) 0.638 g of 40 wt.% TPAOH solution, 0.34 g of 2 wt.% NaAlO2 solution, 0.418 g of 4 wt.% NaOH solution and 0.5 g of anhydrous ethanol were added in sequence into a crucible containing 0.5 g of silica microspheres (the molar ratio of silica, tetrapropylammonium hydroxide, sodium aluminate and sodium hydroxide was 1:0.15:0.01:0.05; the mass ratio of the total mass of tetrapropylammonium hydroxide, sodium aluminate and sodium hydroxide to water was about 1:4). After ultrasonication for 60 min, the mixture was dried at 40 °C for 6 h, and then the temperature was raised to 60 °C and dried for more than 2 h until the reaction precursor solution was completely dried to obtain a dry gel.

[0049] (2) The xerogel was placed in a 150 ml reactor containing 6 g of deionized water and crystallized at 180°C with steam assistance for 24 h. The solid product was removed, centrifuged, washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6 h.

[0050] (3) The sample obtained in step (2) was placed in a 1M ammonium nitrate solution (solid-liquid ratio 1g:25ml) for ammonium exchange, stirred at 80°C for 3h, repeated three times, and then calcined at 550°C for 6h to obtain a hierarchical pore macroporous-microporous ZSM-5 molecular sieve catalyst.

[0051] Figure 6 This is a scanning electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 2 of the present invention. The results show that the sample has a relatively uniform grain size, mainly distributed in the range of 2 to 3 μm, and the grains have a rich macroporous structure.

[0052] Example 3

[0053] A method for preparing a hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst comprises the following steps:

[0054] (1) 0.383 g of 40 wt.% TPAOH solution, 1.7 g of 2 wt.% NaAlO2 solution, 0.418 g of 4 wt.% NaOH solution and 0.5 g of anhydrous ethanol were added in sequence into a crucible containing 0.5 g of silica microspheres (the molar ratio of silica, tetrapropylammonium hydroxide, sodium aluminate and sodium hydroxide was 1:0.09:0.05:0.05; the mass ratio of the total mass of tetrapropylammonium hydroxide, sodium aluminate and sodium hydroxide to water was about 1:11). After ultrasonication for 60 min, the mixture was dried at 40 °C for 6 h, and then the temperature was raised to 60 °C and dried for more than 2 h until the reaction precursor solution was completely dried to obtain a dry gel.

[0055] (2) The xerogel was placed in a 150 ml reactor containing 6 g of deionized water and crystallized at 180°C with steam assistance for 24 h. The solid product was removed, centrifuged, washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6 h.

[0056] (3) The sample obtained in step (2) was placed in a 1M ammonium nitrate solution (solid-liquid ratio 1g:25ml) for ammonium exchange, stirred at 80°C for 3h, repeated three times, and then calcined at 550°C for 6h to obtain a hierarchical pore macroporous-microporous ZSM-5 molecular sieve catalyst.

[0057] Figure 7 This is a scanning electron microscope image of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst prepared in Example 3 of the present invention. The results show that the sample has a relatively uniform grain size, with a particle size distribution of 2 to 3 μm, and the grains have a rich macroporous structure.

[0058] Comparative Example 1

[0059] No sodium hydroxide was added to the reaction precursor solution, and Comparative Example 1 was prepared, which specifically included the following steps:

[0060] (1) 0.638 g of 40 wt.% TPAOH solution, 0.34 g of 2 wt.% NaAlO2 solution, and 0.5 g of anhydrous ethanol were added sequentially into a crucible containing 0.5 g of silica microspheres. After ultrasonication for 60 min, the mixture was dried at 40°C for 6 h, and then heated to 60°C and dried for more than 2 h until the reaction precursor solution was completely dried to obtain a xerogel.

[0061] (2) The xerogel was placed in a 150 ml reactor containing 6 g of deionized water and subjected to steam-assisted crystallization at 180°C for 24 h. The solid product was removed, centrifuged, washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6 h to obtain the sodium molecular sieve of Comparative Example 1.

[0062] Figure 8This is a scanning electron microscope image of the sodium molecular sieve prepared in Comparative Example 1 of the present invention. The results show that the sample does not have a good crystal morphology, with undissolved silica microspheres present and no intracrystalline macroporous structure formed. This suggests that the silica microspheres dissolve too slowly during the crystallization reaction, failing to act as a macroporous template.

[0063] Comparative Example 2

[0064] Excess sodium hydroxide was added to the reaction precursor solution to prepare Comparative Example 2, which included the following steps:

[0065] (1) 0.638 g of 40 wt.% TPAOH solution, 0.34 g of 2 wt.% NaAlO2 solution, 0.836 g of 4 wt.% NaOH solution and 0.5 g of anhydrous ethanol were added sequentially into a crucible containing 0.5 g of silica microspheres. After ultrasonication for 60 min, the mixture was dried at 40°C for 6 h, and then heated to 60°C and dried for more than 2 h until the reaction precursor solution was completely dried to obtain a xerogel.

[0066] (2) The xerogel was placed in a 150 ml reactor containing 6 g of deionized water and subjected to steam-assisted crystallization at 180°C for 24 h. The solid product was removed, centrifuged, washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6 h to obtain the sodium molecular sieve of Comparative Example 2.

[0067] Figure 9 This is a scanning electron microscope image of the sodium molecular sieve prepared in Comparative Example 2 of the present invention. The results show that the sample consists of small crystallites with a particle size of 100-200 nm and no intracrystalline macroporous structure. This indicates that the silica microspheres dissolve too quickly during the crystallization reaction and fail to act as a macroporous template.

[0068] Comparative Example 3

[0069] No ethanol was added to the reaction precursor solution and no ultrasonic treatment was performed to prepare Comparative Example 3. The specific steps are as follows:

[0070] (1) 0.638 g of 40 wt.% TPAOH solution, 0.34 g of 2 wt.% NaAlO2 solution, and 0.418 g of 4 wt.% NaOH solution were sequentially added to a crucible containing 0.5 g of silica microspheres, dried at 40°C for 6 h, and then heated to 60°C and dried for more than 2 h until the reaction precursor solution was completely dried to obtain a xerogel.

[0071] (2) The xerogel was placed in a 150 ml reactor containing 6 g of deionized water and subjected to steam-assisted crystallization at 180°C for 24 h. The solid product was removed, centrifuged, washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6 h to obtain the sodium molecular sieve of Comparative Example 3.

[0072] Figure 10 This is a scanning electron microscope image of the sodium molecular sieve prepared in Comparative Example 3 of the present invention. The results show that the sample consists primarily of crystallites with a size less than 1 μm, with uneven particle size and a small amount of macroporous structure within the crystallites. This indicates that the components of the reaction xerogel are unevenly distributed, and the dissolution-recrystallization rates in different regions of the crystallization reaction are inconsistent, making the template effect of the silica microspheres insignificant.

[0073] Comparative Example 4

[0074] A method for preparing a micron-sized ZSM-5 molecular sieve catalyst comprises the following steps:

[0075] (1) 0.04 g of sodium metaaluminate was dissolved in a mixed solution of 2 g of a 25 wt% aqueous solution of tetrapropylammonium hydroxide and 20 g of deionized water. 10.43 g of tetraethyl orthosilicate was added dropwise with stirring until the solution became clear.

[0076] (2) The clarified solution was aged at 100°C for 3 h and then transferred to a reactor for hydrothermal crystallization at 180°C for 3 days. The resulting solid product was removed, centrifuged, washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6 h to obtain a sodium molecular sieve.

[0077] (3) The sodium molecular sieve obtained in step (2) was placed in a 1M ammonium nitrate solution (solid-liquid ratio 1g:25ml) for ammonium exchange, stirred at 80°C for 3h, repeated three times, and then calcined at 550°C for 6h to obtain a micron-sized ZSM-5 molecular sieve catalyst.

[0078] Figure 11 This is a scanning electron microscope image of the micron-sized molecular sieve catalyst prepared in Comparative Example 4 of the present invention. The results show that the sample is a crystal with a particle size of 3 to 5 μm and a typical coffin-shaped morphology of ZSM-5 molecular sieve.

[0079] Application example: catalytic reaction

[0080] The catalytic performance of the ZSM-5 molecular sieve catalysts prepared in Comparative Example 4 and Example 2 was evaluated by methanol to olefins (MTO) reaction. The reaction was carried out in a fixed bed microreactor. The specific process was as follows:

[0081] The ZSM-5 molecular sieve catalyst was made into 40-60 mesh granules by a tablet press, and 0.2 g was taken and loaded into a reaction tube, and both ends were filled with quartz sand. The catalytic reaction was carried out under normal pressure. Before the reaction, the catalyst was pretreated at 500 ° C for 1 hour under N2 atmosphere, and then the reactor temperature was lowered to the reaction temperature of 480 ° C. Methanol was pumped into a preheating device at 180 ° C to be converted into gas, mixed with N2 at a flow rate of 90 ml / min, and then the mixed gas was passed into the reactor with a feed weight space velocity WHSV = 3.6h -1Sampling was performed every 0.5-1 h. The reaction products were analyzed online using an Agilent 6820 gas chromatograph, and the methanol conversion and ethylene and propylene selectivities at different reaction times were calculated.

[0082] Figure 12 The catalytic performance evaluation results of the ZSM-5 molecular sieve catalysts prepared in Comparative Example 4 and Example 2 of the present invention are shown. In the ZSM-5 molecular sieve catalyst prepared in Comparative Example 4, the methanol conversion rate began to decline after 2 hours of reaction, and the conversion rate decreased to 40% after 4.5 hours of reaction. In the ZSM-5 molecular sieve catalyst prepared in Example 2, the methanol conversion rate began to decline after 6 hours of reaction, and the conversion rate decreased to 40% after 13 hours of reaction. The introduction of the macroporous structure in the ZSM-5 molecular sieve catalyst prepared in the present invention enhances the diffusion and fluidity of reactants, reaction intermediates and reaction products in the molecular sieve, so that the molecular sieve catalyst exhibits a longer catalytic life and slower deactivation behavior, and has stronger anti-deactivation performance.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several improvements and changes can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst, characterized in that The following steps are involved: (1) Tetrapropylammonium hydroxide, sodium metaaluminate, sodium hydroxide, water, and anhydrous ethanol are uniformly mixed to obtain a silicon source treatment solution; silicon oxide microspheres are placed in the silicon source treatment solution as a silicon source and ultrasonically dispersed for 0.5 to 1 h at an ultrasonic power of 50 to 70 W, and then dried to obtain a xerogel; The silicon source is silica microspheres with a particle size of 300 to 600 nm; the molar ratio of silica, tetrapropylammonium hydroxide, sodium aluminate, and sodium hydroxide is 1:(0.06 to 0.15):(0 to 0.05):(0.03 to 0.10), and the sodium aluminate content is not zero; the mass ratio of the total mass of tetrapropylammonium hydroxide, sodium aluminate, and sodium hydroxide to water is 1:(2.5 to 25); and the mass ratio of ethanol to silica microspheres is 1 to 5. (2) steam-assisted crystallization of the dry gel to obtain a solid product, which is then calcined to obtain a hierarchical macroporous-microporous ZSM-5 molecular sieve; (3) exchanging the hierarchical macroporous-microporous ZSM-5 molecular sieve obtained in step (2) with ammonium in an ammonium salt solution, and then calcining to obtain a hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst; The grain size of the hierarchical macroporous-microporous ZSM-5 molecular sieve catalyst is distributed in the range of 1 to 2 μm, the micropore diameter is concentrated in the range of 0.4 to 0.6 nm, the grains have abundant macroporous structures, the macropore structures inside the grains are interconnected, and the macropore diameter is distributed in the range of 300 to 500 nm.

2. The method for preparing a hierarchical macroporous-microporous ZSM-5 molecular sieve according to claim 1, characterized in that In step (1), the drying temperature is 40-60°C.

3. The method for preparing a hierarchical macroporous-microporous ZSM-5 molecular sieve according to claim 1, characterized in that In step (2), the crystallization temperature is 150-180° C., and the crystallization time is 24-72 h.

4. The method for preparing a hierarchical macroporous-microporous ZSM-5 molecular sieve according to claim 1, characterized in that In step (2), the calcination temperature is 500-600° C., and the calcination time is 5-7 hours.

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