Nanoflower-like hzsm-5 molecular sieve, and preparation method and application thereof

Abstract

This invention provides a nano-flower-like HZSM-5 molecular sieve, its preparation method, and its applications. The nano-flower-like HZSM-5 molecular sieve is an aggregate formed by assembling nanorod-shaped particles, and it contains mesopores. The cross-sectional diameter of the nanorod-shaped particles is 5–40 nm. This nano-flower-like HZSM-5 molecular sieve possesses advantages such as high catalytic activity, high selectivity for low-carbon olefins, and long service life.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a nano-flower-like HZSM-5 molecular sieve, its preparation method, and its application. Background Technology

[0002] With rapid economic development and continuous industrial expansion, the demand for low-carbon olefins (such as ethylene and propylene) is increasing. Compared to steam cracking, catalytic cracking offers advantages such as lower energy consumption and less pollution, and has become one of the main methods for producing low-carbon olefins. Catalytic cracking utilizes the principle of shape-selective catalytic cracking to selectively break down reactants into low-carbon olefins. The catalyst is a crucial factor affecting product distribution in catalytic cracking. Therefore, catalysts used in catalytic cracking need to possess high catalytic activity and high selectivity for low-carbon olefins to improve the yield of low-carbon olefins.

[0003] HZSM-5 molecular sieves, with their unique pore structure and high specific surface area, are widely used in the catalytic cracking production of low-carbon olefins. The pore structure and crystal size of HZSM-5 molecular sieves directly affect their catalytic performance and low-carbon olefin selectivity. For example, patent document CN105646562A discloses the preparation of mesoporous ZSM-5 zeolite molecular sieves using diester-based aliphatic chain organosilicon quaternary ammonium salts as template agents; patent document CN104192859A discloses a method of preparing small-crystal ZSM-5 molecular sieves by first nucleating a prepared silica-alumina mixed sol under low-temperature conditions and then crystallizing it at a higher temperature; and patent CN101428818B discloses the synthesis of small-crystal ZSM-5 molecular sieves by adding the organic base isopropylamine to inhibit crystal nucleus growth. However, the catalytic performance and low-carbon olefin selectivity of these HZSM-5 molecular sieves require further improvement.

[0004] Therefore, how to provide an HZSM-5 molecular sieve that exhibits excellent catalytic performance and selectivity for low-carbon olefins is an important issue for those skilled in the art. Summary of the Invention

[0005] The nano-flower-shaped HZSM-5 molecular sieve provided by this invention is formed by assembling nanorod-shaped particles and contains mesopores. This makes the nano-flower-shaped HZSM-5 molecular sieve not only have the advantages of high catalytic activity and high selectivity for low-carbon olefins, but also facilitate the diffusion and transport of reaction raw materials and products, thereby reducing carbon deposition in the molecular sieve channels and extending the service life of the molecular sieve.

[0006] The method for preparing nano-flower-shaped HZSM-5 molecular sieve provided by the present invention can obtain the above-mentioned nano-flower-shaped HZSM-5 molecular sieve, and has the advantages of simple preparation process and easy operation.

[0007] The method for preparing low-carbon olefins provided by this invention utilizes the above-mentioned HZSM-5 molecular sieve as a catalyst for catalytic cracking reaction, and has the advantages of high yield of low-carbon olefins.

[0008] In a first aspect, the present invention provides a nanoflower-like HZSM-5 molecular sieve, wherein the nanoflower-like HZSM-5 molecular sieve is an aggregate formed by assembling nanorod-shaped particles, and the nanoflower-like HZSM-5 molecular sieve contains mesopores, wherein the cross-sectional diameter of the nanorod-shaped particles is 5 to 40 nm.

[0009] According to one embodiment of the present invention, the average particle size of the nanoflower-like HZSM-5 molecular sieve is 1 to 3 μm.

[0010] According to one embodiment of the present invention, the total specific surface area of ​​the nanoflower-like HZSM-5 molecular sieve is 350–450 m². 2 / g, with an external specific surface area of ​​105–121m² 2 / g, with an average pore size of 2.5–29 nm and a micropore volume of 0.12 cm³. 3 / g, mesoporous pore volume is 0.17~0.23cm³ 3 / g, total pore volume is 0.29~0.35cm³ 3 / g.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned nano-flower-like HZSM-5 molecular sieve, comprising the following steps:

[0012] Mix the alkali source, silicon source, template agent, and some water to obtain mixture A; mix the aluminum source and the remaining water to obtain mixture B.

[0013] Solution A, solution B, and organic alcohol amine are mixed to obtain mixture C;

[0014] The mixture C is subjected to a crystallization reaction at 100-200℃ for 1-10 days to obtain mixture D; after filtering, washing and drying the mixture D, the obtained solid product is subjected to a first calcination treatment to obtain ZSM-5 molecular sieve.

[0015] The ZSM-5 molecular sieve is subjected to ion exchange, and then subjected to a second calcination treatment to obtain nano-flower-like HZSM-5 molecular sieve.

[0016] According to one embodiment of the present invention, the organic alcohol amine includes at least one of methanolamine, diethanolamine, triethanolamine, ethanolamine, N,N-diethanolamine, N,N-diethylethanolamine, diisopropanolamine, triethanolamine, triisopropanolamine, and N-methyldiethanolamine.

[0017] According to one embodiment of the present invention, the molar ratio of the alkali source, aluminum source, and silicon source is (1-30):(0-2):100; wherein the alkali source is calculated as Na2O or K2O, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2.

[0018] According to one embodiment of the present invention, the molar ratio of template agent to silicon source is (7-15):100.

[0019] According to one embodiment of the present invention, the molar ratio of water to silicon source is (1200-1800):100, wherein the water includes a portion of water and the remainder.

[0020] According to one embodiment of the present invention, the structural formula of the template agent is shown in Formula 1:

[0021]

[0022] In Equation 1, n = 14 to 22; and / or,

[0023] The silicon source includes at least one of water glass, silicic acid, silica sol, fumed silica, silica, methyl orthosilicate, and tetraethyl orthosilicate; and / or,

[0024] The aluminum source includes at least one of sodium aluminate, aluminum isopropoxide, aluminum sulfate, aluminum trichloride, sodium aluminate, aluminum nitrate, aluminum hydroxide, boehmite, and pseudoboehmite; and / or,

[0025] The alkaline source includes at least one of sodium hydroxide and potassium hydroxide.

[0026] A third aspect of the present invention provides a method for preparing low-carbon olefins, comprising: subjecting n-heptane feedstock to a catalytic cracking reaction in the presence of a catalyst to obtain low-carbon olefins; wherein the catalyst comprises the above-mentioned nano-flower-like HZSM-5 molecular sieve.

[0027] The implementation of this invention has at least the following beneficial effects:

[0028] The present invention provides a nano-flower-like HZSM-5 molecular sieve, which is an aggregate formed by assembling nanorod-shaped particles and has a mesoporous structure. On the one hand, compared with large crystallites, the nanorod-shaped particles have smaller crystallites, and the molecular sieve assembled from nanorod-shaped particles has a larger external specific surface area, thereby exposing more active centers on the outer surface and giving the molecular sieve excellent catalytic performance. On the other hand, due to the presence of mesopores and the shorter channels of the small crystallites, the diffusion resistance of reactant and product molecules within the channels is small, and product molecules can diffuse out of the channels quickly, avoiding the occurrence of side reactions. This is beneficial to improving the selectivity of low-carbon olefins. In addition, it is also beneficial to reduce carbon deposition in the channels and extend the service life of the molecular sieve. Attached Figure Description

[0029] Figure 1 This is the XRD pattern of the HZSM-5 molecular sieve in Example 1 of this invention;

[0030] Figure 2 This is a SEM image of the HZSM-5 molecular sieve in Example 1 of this invention;

[0031] Figure 3 This is a SEM image of the HZSM-5 molecular sieve in Example 2 of this invention;

[0032] Figure 4 This is a SEM image of the HZSM-5 molecular sieve in Example 3 of this invention;

[0033] Figure 5 This is a TEM image of the molecular sieve in Example 1 of the present invention;

[0034] Figure 6 This is a TEM image of the molecular sieve in Example 2 of the present invention;

[0035] Figure 7 This is a TEM image of the molecular sieve in Example 3 of the present invention;

[0036] Figure 8 These are N2 adsorption-desorption isotherms of the molecular sieves in Examples 1, 2 and 3 of this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] In a first aspect, the present invention provides a nano-flower-like HZSM-5 molecular sieve, which is an aggregate formed by assembling nanorod-shaped particles and contains mesopores, wherein the cross-sectional diameter of the nanorod-shaped particles is 5 to 40 nm.

[0039] In this invention, the nano-flower-like HZSM-5 molecular sieve has a porous structure. In addition to possessing the microporous structure (pore size < 2 μm) of traditional molecular sieves, this HZSM-5 molecular sieve also exhibits a mesoporous structure (pore size 2–50 μm), which is beneficial for promoting the diffusion and transport of reactants and products.

[0040] According to the technical solution provided by this invention, when using the nano-flower-like HZSM-5 molecular sieve as a catalyst to prepare low-carbon olefins, it exhibits excellent catalytic performance, low-carbon olefin selectivity, and a long service life. Based on this phenomenon, the inventors analyzed it and believe it may be due to the following: Firstly, compared to large crystallites, the nanorod-shaped particles are smaller in size. Therefore, the molecular sieve assembled from nanorod-shaped particles has a larger external specific surface area, resulting in more active centers exposed on the outer surface, thus giving the molecular sieve excellent catalytic performance. Secondly, due to the presence of mesopores and the shorter channels of the small crystallites, the diffusion resistance of reactant and product molecules within the channels is low, and products can quickly diffuse out of the channels, avoiding side reactions and improving the selectivity of low-carbon olefins. Furthermore, it also helps reduce carbon deposition in the channels, extending the service life of the molecular sieve.

[0041] Besides enhancing catalytic performance, low-carbon olefin selectivity, and extending service life, it is worth mentioning that the nano-flower-like HZSM-5 molecular sieve of this invention also has the advantage of controllable performance. This is because, during the preparation of the nano-flower-like HZSM-5 molecular sieve, the physicochemical properties such as the silica-alumina ratio, specific surface area, pore structure, acid density, and cross-sectional diameter (also known as grain size) of the nanorod-shaped particles can be flexibly adjusted by controlling parameters such as raw material selection and preparation conditions, thereby modulating its catalytic performance and low-carbon olefin selectivity.

[0042] Therefore, the unique composition and structure of the nano-flower-like HZSM-5 molecular sieve of this invention can ultimately ensure that the nano-flower-like HZSM-5 molecular sieve has crystals and mesopores of a specific size by controlling parameters such as raw material selection and preparation conditions. This controllability not only enables consistency of products in the same batch and improves production efficiency, but also facilitates the construction of nano-flower-like HZSM-5 molecular sieves with differences in crystal size, thereby achieving product diversity and meeting the different needs of different environments for catalytic performance, selectivity of low-carbon olefins, etc.

[0043] The present invention does not limit the average particle size of the nanoflower-shaped HZSM-5 molecular sieve. In one embodiment, the average particle size of the nanoflower-shaped HZSM-5 molecular sieve is 1 to 3 μm, for example, 1 μm, 1.5 μm, 2.4 μm, 3 μm or any combination thereof.

[0044] This invention does not limit the specific surface area, pore size, pore volume and other physicochemical properties of the nanoflower-shaped HZSM-5 molecular sieve, as long as the nanoflower-shaped HZSM-5 molecular sieve is an aggregate formed by the assembly of nanorod-shaped particles and contains mesopores.

[0045] In one embodiment, the total specific surface area of ​​the nanoflower-like HZSM-5 molecular sieve is 350–450 m². 2 / g, with an external specific surface area of ​​105–121m² 2 / g, with an average pore size of 2.5–29 nm and a micropore volume of 0.12 cm³. 3 / g, mesoporous pore volume is 0.17~0.23cm³ 3 / g, total pore volume is 0.29~0.35cm³ 3 / g. The total specific surface area refers to the sum of the external surface area and the surface area of ​​the internal pore structure of the HZSM-5 nano-flower-shaped molecular sieve per unit mass; the external specific surface area refers to the external surface area of ​​the HZSM-5 nano-flower-shaped molecular sieve per unit mass; and the average pore size is the pore size obtained by dividing the total pore volume of the HZSM-5 nano-flower-shaped molecular sieve by its total specific surface area.

[0046] A second aspect of the present invention provides a method for preparing the aforementioned nanoflower-like HZSM-5 molecular sieve of the first aspect, comprising the following steps:

[0047] (1) Mix the alkali source, silicon source, template agent and some water to obtain mixture A; mix the aluminum source and the remaining water to obtain mixture B;

[0048] (2) Mix solution A, solution B and organic alcohol amine to obtain mixture C;

[0049] (3) Crystallize the mixture C at 100-200℃ for 1-10 days to obtain the mixture D; after filtering, washing and drying the mixture D, perform a first calcination treatment on the obtained solid product to obtain ZSM-5 molecular sieve.

[0050] (4) The ZSM-5 molecular sieve is subjected to ion exchange and then subjected to a second calcination treatment to obtain nano-flower-like HZSM-5 molecular sieve.

[0051] This invention employs a one-step in-situ synthesis of the molecular sieve, which is simple and efficient, and enables the molecular sieve to possess excellent properties such as good catalytic activity and selectivity for low-carbon olefins. Specifically, the molecular sieve can effectively catalyze the cracking of alkanes to produce low-carbon olefins, and is not prone to carbon deposition and deactivation during the reaction, thus having a long service life. At the same time, it can enable the reaction to achieve a high yield of low-carbon olefins.

[0052] Specifically, in the implementation of this invention, in step (1), the template agent and the alkali source are generally added to a portion of water and stirred in a constant temperature water bath at 20–80°C for 0.5–2 hours to obtain a mixture A1. Then, a silicon source is added dropwise to the mixture A1 and stirred in a constant temperature water bath at 20–80°C for 0.5–2 hours to obtain a mixture A. The above operating conditions can disperse and mix the template agent, alkali source, and silicon source evenly, which is more conducive to obtaining a molecular sieve with the above-mentioned excellent properties. Taking into account factors such as molecular sieve performance and reaction efficiency, the stirring temperature can be further set to 40–60°C, and the stirring time can be further set to 0.5–4 hours.

[0053] In step (1), the aluminum source is added to the remaining water and stirred in a constant temperature water bath at 20-80℃ for 0.5-2 hours to obtain mixture B. Considering factors such as the performance of the molecular sieve and the reaction efficiency, the stirring temperature can be further increased to 40-60℃ and the stirring time can be further increased to 0.5-4 hours.

[0054] In step (2) above, solution B is generally added to solution A first, followed by the addition of an organic alcohol amine as a nucleating agent. The mixture is then stirred in a constant temperature water bath at 20–80°C for 1–24 hours to obtain a mixed solution C. These operating conditions allow the raw materials to be dispersed and mixed evenly, which is more conducive to obtaining molecular sieves with the aforementioned excellent properties. Considering factors such as molecular sieve performance and reaction efficiency, the stirring temperature can be further increased to 40–60°C, and the stirring time can be further increased to 0.5–4 hours.

[0055] Furthermore, the present invention can further optimize the following conditions to facilitate the synthesis of the molecular sieve with the above-mentioned excellent properties: In step (2), the mixture C can be stirred in a constant temperature water bath at 20-80°C for 0.5-2 hours. The stirring temperature can be further improved to 40-60°C, and the stirring time can be further improved to 0.5-4 hours.

[0056] In step (3), the mixture C is subjected to hydrothermal crystallization reaction at 100-200℃ for 1-10 days, and can be further subjected to hydrothermal crystallization reaction at 120-170℃ for 3-5 days to obtain mixture D.

[0057] Under normal circumstances, in step (3), the mixture D is cooled to room temperature, filtered, the filter cake is washed, and then dried to obtain the above solid product; wherein, the drying temperature can be 60 to 80°C and the time is 24 to 48 hours.

[0058] Specifically, in this invention, the product obtained in step (3) is ZSM-5 molecular sieve. In specific implementation, the first calcination treatment can generally include: heating the solid product to 500-550°C and calcining it for 4-6 hours to obtain ZSM-5 molecular sieve.

[0059] The ZSM-5 molecular sieve described above can be ion-exchanged to obtain HZSM-5 molecular sieve. In the specific implementation of this invention, ammonium salt solution can generally be used for ammonium exchange. The concentration of the ammonium salt solution can be 0.5-1 mol / L, the ammonium exchange temperature can be 60-100℃, and the ammonium exchange time is 4 hours. The ammonium salt can be a commonly used ammonium salt in the art, such as ammonium nitrate or ammonium chloride.

[0060] After ion exchange, the exchange products are usually dried, for example, at 60-100℃ for 24-48 hours. In practice, the above ion exchange and drying steps are usually performed 1-3 times, and then the exchange products are subjected to a second calcination treatment.

[0061] After ion exchange and a second calcination treatment, HZSM-5 molecular sieve (i.e., hydrogen-form ZSM-5 molecular sieve) is obtained. Specifically, in the implementation of this invention, the second calcination treatment generally includes: heating the exchange product to 500-550℃ and calcining for 4-6 hours to obtain HZSM-5 molecular sieve.

[0062] In general, HZSM-5 molecular sieves can also be shaped and processed to make them easier to use. In one embodiment of the present invention, it may further include: after performing a second calcination treatment on the exchange product, the calcined product is pressed into tablets, crushed and sieved to obtain molecular sieve particles of 40-60 mesh, which can be directly filled into the reaction tube as a catalyst.

[0063] This invention does not limit the amount of alkali source, water, silicon source, aluminum source, template agent, and organic alcohol amine. The amount can be adjusted according to actual needs. By adjusting the amount of organic alcohol amine, alkali source, water, silicon source, aluminum source, and preparation parameters such as crystallization reaction, the physicochemical properties of the nano-flower-like HZSM-5 molecular sieve, such as silicon-aluminum ratio, crystal size, specific surface area, pore structure, and acid density, can be flexibly modified, thereby modifying its catalytic performance.

[0064] In one embodiment, the molar ratio of the alkali source, aluminum source, and silicon source is (1-30):(0-2):100; wherein the alkali source is calculated as Na2O or K2O, the aluminum source as Al2O3, and the silicon source as SiO2. This is beneficial for preparing the above-mentioned nano-flower-like HZSM-5 molecular sieve and giving the molecular sieve superior catalytic performance. The molar ratio of the template agent to the silicon source is (7-15):100; the molar ratio of water to the silicon source is (1200-1800):100, wherein the water is the sum of the partial water and the remaining water in step (1).

[0065] In one embodiment of the present invention, the organic alcohol amine includes at least one of methanolamine, diethanolamine, triethanolamine, ethanolamine, N,N-diethanolamine, N,N-diethylethanolamine, diisopropanolamine, triethanolamine, triisopropanolamine, and N-methyldiethanolamine.

[0066] The inventors believe that the above-mentioned organic alcohol amines can be used to prepare nano-flower-like HZSM-5 molecular sieves assembled from nanorod-shaped particles. Furthermore, since organic alcohol amines have a strong ability to complex and coordinate aluminum species, the surface of the molecular sieve is enriched with aluminum, which is beneficial to increasing the acid density of the molecular sieve. As a result, the above-mentioned catalyst exhibits good catalytic performance in the reaction of catalytic cracking of alkanes to produce low-carbon olefins.

[0067] In this invention, the silicon source is generally selected from at least one of water glass, silicic acid, silica sol, fumed silica, silica, methyl orthosilicate, and / or the alkali source is selected from at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide, and / or the aluminum source may be selected from at least one of sodium aluminate, aluminum isopropoxide, aluminum sulfate, aluminum trichloride, sodium aluminate, aluminum nitrate, aluminum hydroxide, boehmite, and pseudoboehmite.

[0068] In this invention, the template agent can be selected from gemini quaternary ammonium salt surfactants, with the structural formula shown in Formula 1:

[0069]

[0070] In Equation 1, n = 14 to 22.

[0071] A third aspect of the present invention provides a method for preparing low-carbon olefins, comprising: subjecting n-heptane feedstock to a catalytic cracking reaction in the presence of a catalyst to obtain low-carbon olefins; wherein the catalyst comprises the aforementioned nano-flower-like HZSM-5 molecular sieve.

[0072] Specifically, the above-mentioned catalytic cracking reaction conditions can generally be: temperature of 400-700℃, pressure of 0.1-1MPa, and feed rate of 2-10mL / h.

[0073] In the implementation of this invention, the above-mentioned catalytic cracking reaction can generally be carried out in a fixed-bed reactor. Specifically, a dilution gas can be first introduced into a fixed-bed reactor packed with catalyst, and then the reactant (n-heptane) can be introduced and mixed with the dilution gas before entering the fixed-bed reactor packed with catalyst for catalytic cracking reaction. The flow rate of the dilution gas can be controlled to be 100-400 mL / min. This invention does not impose any particular limitation on the dilution gas used; it can be a commonly used dilution gas in the art, such as nitrogen (N2).

[0074] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0075] Example 1

[0076] (1) Add 0.4g of gemini quaternary ammonium salt surfactant and 0.15g of alkali source to 3.0g of deionized water, stir in a constant temperature water bath at 60℃ for 2h, then add 5.2g of tetraethyl orthosilicate dropwise, and continue stirring in a constant temperature water bath at 60℃ for 2h to form mixture A; add 0.1g of aluminum isopropoxide to 18g of deionized water, stir in a constant temperature water bath at 60℃ until completely dissolved to form mixture B; wherein, the gemini quaternary ammonium salt surfactant is [C n H 2n+1 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 ]Br2, where n is 18;

[0077] (2) Add mixture B dropwise to mixture A, continue stirring for 12 hours, then add 1.5g of ethanolamine and continue stirring until homogeneous to form mixture C;

[0078] (3) The mixture C was transferred to a stainless steel crystallization kettle lined with polytetrafluoroethylene and crystallized at 150°C for 4 days. After filtration and drying at 100°C for 24 hours, molecular sieve raw powder was obtained. The molecular sieve raw powder was placed in a muffle furnace and calcined at 550°C for 6 hours to remove the template agent, and sodium-type ZSM-5 molecular sieve was obtained.

[0079] (4) The above-mentioned sodium-type ZSM-5 molecular sieve was subjected to ammonium exchange three times in a 1M ammonium nitrate solution (heated and stirred in a water bath at 80°C for 4 hours), filtered, washed, and calcined at 550°C for 4 hours to obtain the HZSM-5 molecular sieve of this embodiment.

[0080] Example 2

[0081] The preparation method of HZSM-5 molecular sieve in this embodiment is basically the same as that in Example 1. The difference is that the raw materials and the proportion of raw materials in step (2) are different. Specifically, mixture B is added dropwise to mixture A and stirred for 12 hours. Then, 2.4g of triisopropanolamine is added and stirred until uniform to form mixture C. The mixture C in step (3) is replaced with the mixture C in this embodiment, and other conditions remain unchanged.

[0082] Example 3

[0083] The preparation method of HZSM-5 molecular sieve in this embodiment is basically the same as that in Example 1. The difference is that the raw materials and the proportion of raw materials in step (2) are different. Specifically, mixture B is added dropwise to mixture A and stirred for 12 hours. Then, 3.4g of triethanolamine is added and stirred until uniform to form mixture C. The mixture C in step (3) is replaced with the mixture C in this embodiment, and other conditions remain unchanged.

[0084] Comparative Example 1

[0085] The preparation method of HZSM-5 molecular sieve in Comparative Example 1 is basically the same as that in Example 1. The difference is that the gemini quaternary ammonium salt surfactant is not added in step (1). Other conditions remain unchanged. The molecular sieve product obtained is an amorphous structure as determined by XRD.

[0086] Comparative Example 2

[0087] Commercial ZSM-5 molecular sieve, purchased from Nankai Catalyst Factory, with a silicon-to-aluminum ratio (SiO2 / Al2O3) of 100.

[0088] Experimental example:

[0089] I. Morphological and structural characterization and texture property testing of molecular sieves

[0090] The surface morphology and structure of the molecular sieve were characterized by XRD, SEM, TEM, and N2 adsorption-desorption.

[0091] Figure 1 This is the XRD pattern of the molecular sieve in Example 1 of this invention. Figure 2 This is a SEM image of the molecular sieve sample from Example 1; Figure 3 This is an SEM image of the molecular sieve in Example 2; Figure 4 This is an SEM image of the molecular sieve in Example 3 of this invention. Figure 5 This is a TEM image of the molecular sieve in Example 1 of the present invention. Figure 6 This is a TEM image of the molecular sieve in Example 2 of the present invention. Figure 7 This is a TEM image of the molecular sieve in Example 3 of the present invention. Figure 8 Table 1 shows the N2 adsorption-desorption curves of the molecular sieve samples in Examples 1, 2, and 3 of this invention. Table 1 shows the texture properties of the HZSM-5 molecular sieve in Examples 1-3.

[0092] II. Molecular sieve performance testing:

[0093] HZSM-5 molecular sieve was compressed, crushed, and sieved to obtain a molecular sieve sample of 40-60 mesh. 0.75 g of the molecular sieve sample was weighed and placed in a stainless steel tube reaction tube to form a catalyst bed. The volumetric flow rate of dilution gas nitrogen was adjusted to 400 mL / min and continuously introduced into the reactor for 0.5 h. Heating was then turned on. After the temperature in the reaction tube stabilized to the reaction temperature, 2 mL / h of n-heptane was introduced. After being vaporized in the preheating section at the top of the reaction tube, it came into contact with the catalyst bed to undergo a catalytic cracking reaction. The reaction products were collected online and the composition and content of the products were analyzed by gas chromatography. The reaction temperature range was 400-650℃.

[0094] The reaction product distribution of Example 1 is shown in Table 2, and the reaction product distribution of Comparative Example 2 is shown in Table 3.

[0095] Table 1

[0096]

[0097] In Table 1: 1)S BET 1) BET specific surface area with relative pressure (P / P0) between 0.05 and 0.20; 2) S ext It is the external specific surface area obtained according to the t-plot method; 3) V tol The total pore volume is obtained by P / P0 = 0.95; 4) V micro The micropore volume is obtained based on the t-plot method; 5) Pore size is the average pore size obtained from BJH adsorption data, and the two values ​​represent different mesopore size distribution ranges.

[0098] Table 2

[0099]

[0100] Table 3

[0101]

[0102] In Tables 2 and 3, C1, C2, and C2 ＝ C3, C3 ＝ C4, C4 ＝ They represent methane, ethane, ethylene, propane, propylene, butane, and butene, respectively; "BTX" represents benzene, toluene, and xylene; and "C2" represents... ＝ +C3 ＝ "Represents ethylene and propylene."

[0103] In Table 3, the contents of feedstocks and products in the catalytic cracking reaction of hydrocarbons were quantitatively analyzed using the area normalization method. The conversion rate (X) of the feedstock and the yield (Y) of the product were calculated using the following formulas 1-3. Taking n-heptane as an example:

[0104]

[0105]

[0106] In the formula, mC7H 16,in This represents the mass fraction of n-heptane entering; mC7H 16,out The mass fraction of n-heptane after the reaction; C x H y It is a cracking product of n-heptane; m(C x H y ) is C x H y Mass fraction of pyrolysis products; x is the number of carbon atoms in the pyrolysis products; y is the number of hydrogen atoms in the pyrolysis products.

[0107] according to Figure 1 It can be seen that the XRD pattern of the molecular sieve in Example 1 shows characteristic diffraction peaks of the MFI topology at 8°, 9°, 23° and 25°, indicating that the molecular sieve in Example 1 has a typical MFI framework structure and does not contain other impurity peaks, proving that the HZSM-5 molecular sieve in Example 1 has high purity and quality.

[0108] according to Figure 2 It is known that the morphology of HZSM-5 molecular sieve is a nanoflower-like structure, formed by the assembly of nanorod-like particles, wherein the cross-sectional diameter of the nanorod-like particles is approximately 10-15 nm, and the HZSM-5 molecular sieve is a flower-like microsphere with a hierarchical porous structure. Specifically, the molecular sieve of Example 1 is a flower-like microsphere with a particle size of 1.5 μm formed by the cross-assembly of nanorods. Figure 8 As can be seen from the hysteresis loop in the N2 adsorption-desorption curve of the molecular sieve in the embodiment, it indicates that there is a mesoporous structure in the ZSM-5 molecular sieve provided by the present invention. It is a mesoporous-microporous composite hierarchical pore structure. The inventors believe that the mesopores may be intercrystalline mesopores formed by the accumulation of nanorod-shaped particles in the HZSM-5 molecular sieve.

[0109] according to Figure 3 It is known that the molecular sieve in Example 2 is an aggregate of nanoflower-shaped molecular sieves with a cross-sectional diameter of about 1.5 μm, which is formed by assembling nanorod-shaped particles with a cross-sectional diameter of about 20 nm.

[0110] according to Figure 4 It can be seen that the molecular sieve in Example 3 is formed by assembling nanorod-shaped particles with a cross-sectional diameter of about 40 nm into regular flower-shaped microspheres with a particle size of about 2.4 μm, and the nanorod-shaped particles are tightly assembled together.

[0111] As shown in Tables 2 and 3, the HZSM-5 molecular sieve provided by this invention has excellent catalytic activity and low-carbon olefin selectivity, and can obtain a high yield of low-carbon olefins (including ethylene and propylene).

[0112] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a nanoflower-like HZSM-5 molecular sieve, characterized in that, The preparation method comprises the following steps: mixing an alkali source, a silicon source, a template agent and part of water to obtain a mixed solution A; mixing an aluminum source and the rest of water to obtain a mixed solution B; mixing solution A, solution B and an organic alcohol amine to obtain a mixed solution C; crystallizing the mixed solution C at 100-200 ℃ for 1-10 days to obtain a mixed solution D; filtering, washing and drying the mixed solution D, and then performing first calcination on the obtained solid product to obtain ZSM-5 molecular sieve; performing ion exchange on the ZSM-5 molecular sieve, and then performing second calcination to obtain nanoflower-shaped HZSM-5 molecular sieve; the nanoflower-shaped HZSM-5 molecular sieve is an aggregate formed by nanorod-shaped particles, and the nanoflower-shaped HZSM-5 molecular sieve contains mesopores, wherein the cross-sectional diameter of the nanorod-shaped particles is 5-40 nm; the template agent has a structural formula as shown in formula 1: Formula 1 in formula 1, n=14-22.

2. The production method according to claim 1, characterized by, The organic alcohol amine includes at least one of methanol amine, dimethyl alcohol amine, trimethyl alcohol amine, ethanol amine, N,N diethanol amine, N,N diethyl ethanol amine, diisopropyl alcohol amine, triethanol amine, triisopropyl alcohol amine and N-methyl diethanol amine.

3. The production method according to claim 1 or 2, characterized by, The molar ratio of the alkali source, the aluminum source and the silicon source is (1-30):(0-2):100; wherein the alkali source is calculated based on Na2O, the aluminum source is calculated based on Al2O3 and the silicon source is calculated based on SiO2.

4. The production method according to claim 1 or 2, characterized by, The molar ratio of the template agent and the silicon source is (7-15):

100.

5. The production method according to claim 1 or 2, characterized by, The molar ratio of water and the silicon source is (1200-1800):100, wherein the water includes part of water and the rest of water.

6. The preparation method according to claim 1 or 2, characterized in that, the silicon source includes at least one of water glass, silicic acid, silica sol, fumed silica, white carbon black, methyl orthosilicate and tetraethyl orthosilicate; and / or the aluminum source includes at least one of sodium aluminate, aluminum isopropoxide, aluminum sulfate, aluminum chloride, sodium metaaluminate, aluminum nitrate, aluminum hydroxide, pseudo-boehmite, boehmite and pseudo-boehmite; and / or the alkali source includes at least one of sodium hydroxide and potassium hydroxide.

7. The production method according to claim 1 or 2, characterized by, The average particle size of the nanoflower-shaped HZSM-5 molecular sieve is 1-3 μm.

8. The production method according to claim 1 or 2, characterized by, The total specific surface area of the nanoflower-shaped HZSM-5 molecular sieve is 350-450 m 2 / g, the external specific surface area is 105-121 m 2 / g, the average pore size is 2.5-29 nm, the micropore volume is 0.12 cm 3 / g, the mesopore volume is 0.17-0.23 cm 3 / g, and the total pore volume is 0.29-0.35 cm 3 / g.

9. A process for the production of lower olefins, characterized by, The preparation method comprises the following steps: performing catalytic cracking on a n-heptane raw material under the action of a catalyst to obtain low-carbon olefins; wherein the catalyst comprises the nanoflower-shaped HZSM-5 molecular sieve prepared by the preparation method of the nanoflower-shaped HZSM-5 molecular sieve according to any one of claims 1-8.

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