A method for preparing a zsm-5 molecular sieve

Abstract

The application discloses a preparation method of ZSM-5 molecular sieve, which comprises the following steps: mixing a silicon source, an aluminum source, a template agent and water to form a gel, and then performing crystallization, filtration, washing, drying and calcination to obtain the ZSM-5 molecular sieve; wherein the silicon source is amorphous silicon dioxide treated by alkali. The ZSM-5 molecular sieve synthesized by the method has abundant mesoporous structures and good hydrothermal stability, and the relative content of micropore and mesopore pore volume can be adjusted according to requirements.

Description

Technical Field

[0001] This invention relates to a method for preparing ZSM-5 molecular sieves, and more specifically to a method for preparing microporous ZSM-5 molecular sieves in one step. Background Technology

[0002] Since its synthesis in the late 1960s, the microporous molecular sieve ZSM-5 has been widely used in various fields such as petrochemicals, modern coal chemicals, fine chemicals, and environmental protection, thanks to its wide range of tunable acid properties and good thermal and hydrothermal stability. With the continuous changes in market demand, traditional microporous ZSM-5 molecular sieves, due to the limitation of pore size, have encountered difficulties in processing reactions containing macromolecules. Reactants struggle to diffuse into the pores and contact the active centers, leading to a significant reduction in reaction efficiency. Furthermore, some reaction products cannot escape the pores in time, easily causing secondary reactions. Therefore, in order to further expand the application range of ZSM-5 molecular sieves, researchers have been actively developing technologies to introduce mesopores or macropores into microporous ZSM-5 molecular sieves in recent years.

[0003] CN102125868A describes the synthesis of microporous ZSM-5 molecular sieves using an organic template agent, followed by alkali treatment to obtain a micro-mesoporous composite ZSM-5 molecular sieve. This is a conventional method for introducing mesopores into microporous molecular sieves, which can yield a larger mesoporous specific surface area, but it easily damages the microporous structure of the molecular sieve.

[0004] CN103071522A discloses a method for preparing a catalytic cracking catalyst with hierarchical ZSM-5 molecular sieve as the main acidic component. The method uses a combination of dual template agents—microporous template agent tetrapropylammonium hydroxide and mesoporous template agent cetyltrimethylammonium bromide—to crystallize in two steps to obtain hierarchical ZSM-5 molecular sieve with pore size of 0.5-30 nm.

[0005] CN107303498A discloses a low-carbon alkane dehydrogenation catalyst using hierarchical ZSM-5 molecular sieves and alumina as supports. The ZSM-5 molecular sieve with a mesopore size of 4-10 nm is prepared using water glass, dihydroxyethylcyclohexylamine, aluminum sulfate, concentrated sulfuric acid, sodium chloride, and deionized water as raw materials. While the preparation method is simple, it requires a large amount of concentrated sulfuric acid, necessitates sophisticated synthesis equipment, and the high cost of the template agent limits its large-scale application.

[0006] CN108975351A discloses a method for synthesizing hierarchically porous ZSM-5 zeolite microspheres with a diameter of 11~15µm in a NaOH-water-ethanol crystallization system using a long-chain alkyltrimethylammonium bromide surfactant as a template agent. Since these microspheres are composed of uniformly sized and morphologically packed nanorods, it is difficult to determine the content of intracrystalline and intercrystalline mesopores, thus affecting in-depth research on their structure-property relationship.

[0007] CN109678174 discloses a hierarchical porous ZSM-5 molecular sieve and its application in the etherification of 2,5-furandiethanol with a monohydric alcohol to prepare 2,5-furandiethanol dimethyl ether. The method involves preparing a dry gel from raw materials containing a silicon source, an aluminum source, a template agent, and an alcohol compound, followed by crystallization in a water-containing reactor to obtain a hierarchical porous ZSM-5 molecular sieve with an average mesopore size of 2-6 nm and a mesopore volume of 0.4-0.6 mL / g. However, this method uses hexadecyltrimethoxysilane, hexadecyltriethoxysilane, and octadecyltrimethoxysilane as silicon sources, which are expensive and not conducive to industrial production.

[0008] The method disclosed in CN108328625 involves first mixing a surfactant, water, inorganic alkali, and aluminum source evenly, then adding a silicon source dropwise, stirring at 70-90°C, adding an organic template agent, and continuing stirring at 70-90°C. The mixture is then hydrothermally crystallized and calcined to prepare a hierarchical porous ZSM-5 molecular sieve. However, because the prepared molecular sieve has a hollow structure, its morphology can be destroyed during subsequent catalyst preparation processes such as mixing and extrusion.

[0009] Therefore, developing a simple and low-cost preparation route for micro-mesoporous composite ZSM-5 molecular sieves to produce micro-mesoporous ZSM-5 molecular sieves with stable mesoporous structure and excellent performance is of great significance to the development of the petrochemical industry. Summary of the Invention

[0010] To overcome the shortcomings of the prior art, the present invention provides a method for preparing ZSM-5 molecular sieve. The ZSM-5 molecular sieve synthesized by the method has a rich mesoporous structure and good hydrothermal stability. At the same time, the relative content of micropores and mesopore volumes can be adjusted according to requirements.

[0011] A method for preparing ZSM-5 molecular sieve involves mixing a silicon source, an aluminum source, a template agent, and water to form a gel, followed by crystallization, filtration, washing, drying, and calcination to obtain ZSM-5 molecular sieve; wherein the silicon source is amorphous silica treated with alkali.

[0012] In the above method, the molar ratio of silicon source (as SiO2): aluminum source (as Al2O3): template agent: H2O in the gel is 1:(0.003~0.05):(0.05~0.50):(20~60); preferably, the molar ratio of silicon source (as SiO2): aluminum source (as Al2O3): template agent: H2O in the gel is 1:(0.005~0.05):(0.08~0.40):(25~50).

[0013] In the above method, ZSM-5 molecular sieve is obtained by gelling at 150~200 °C, preferably 160~180 °C, crystallizing for 6~36 hours, preferably 8~32 hours, and then filtering, washing, drying and calcining.

[0014] In the above method, the amorphous silica has a specific surface area of ​​600~1300 m². 2 / g, preferably 700~1200m 2 / g; pore volume is 0.6~1.3 cm³ 3 / g, preferably 0.7~1.2 cm 3 / g; pore diameter is 1~15 nm, preferably 2~10 nm.

[0015] The amorphous silica preparation process described above is as follows: a silicon source is added to deionized water and dispersed evenly, then a surfactant is added and stirred; the pH of the solution is adjusted to 1-5, preferably 1.5-4, and then heated in a water bath for a period of time; after filtration, washing, drying, and calcination, amorphous silica is obtained.

[0016] In the above-mentioned preparation process of amorphous silica, the silicon source is an inorganic silicon source, preferably one or more of water glass, silica sol, or silica.

[0017] In the above-mentioned preparation process of amorphous silica, the surfactant is one or more of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, and octadecyltrimethylammonium bromide.

[0018] In the above-mentioned preparation process of amorphous silica, the molar ratio of the silicon source (SiO2) to the surfactant is 1:(0.02~0.3), preferably 1:(0.05~0.2).

[0019] In the above-mentioned preparation process of amorphous silica, the molar ratio of the silicon source (SiO2) to deionized water is 1:(30~300), preferably 1:(50~220).

[0020] In the above-mentioned preparation process of amorphous silica, the heating temperature is 30~80°C, preferably 40~70°C, and the heating time is 0.5~8 hours, preferably 1~6 hours.

[0021] In the above method, the alkali treatment involves adding the prepared or selected amorphous silica to an alkaline solution and heating and stirring. The alkali treatment uses an inorganic alkali, which is one or more of ammonia, sodium hydroxide, and potassium hydroxide, with ammonia being preferred. The heating and stirring time for the alkali treatment is 0.5–12 hours, preferably 2–8 hours; the heating temperature is 25–60 °C, preferably 30–50 °C. The alkali treatment uses OH... - The molar ratio of inorganic alkali to amorphous silica (based on SiO2) is 0.30 to 1.12, preferably 0.35 to 1.0.

[0022] In this invention, water glass is used as the initial silicon source. With the assistance of a surfactant, mesoporous amorphous silica is prepared. When this silica is used as the silicon source for the subsequent synthesis of ZSM-5 molecular sieves, it possesses a relatively regular mesoporous structure but has not yet highly crystallized into a stable crystalline phase. After further treatment in an alkaline solution for a period of time, some of the -Si-O- bonds open, which facilitates the formation of -Si-O-Al- bonds in the subsequent molecular sieve structure. However, most of the mesoporous structure is retained. Furthermore, under the action of a microporous template agent in a suitable ZSM-5 molecular sieve synthesis system, a microporous structure is generated, and the mesoporous structure further crystallizes and stabilizes, thus obtaining a micro-mesoporous composite ZSM-5 molecular sieve. Moreover, the degree of retention of the mesoporous structure varies with the degree of alkaline treatment of the mesoporous amorphous silica; therefore, the relative content of mesopores and micropores in the resulting composite molecular sieve can be adjusted according to requirements. This method is simple to operate, requires less surfactant and microporous template dosage, has low cost, and produces molecular sieve products with excellent performance, making it a feasible industrial production route.

[0023] In the above method, the drying temperature is 80~120 °C, the drying time is 4~12 hours, the calcination temperature is 500~600 °C, and the calcination time is 2~6 hours.

[0024] A ZSM-5 molecular sieve prepared by the above method, wherein the mesopore volume with a pore size of 2~6nm accounts for 50~92% of the total pore volume of the molecular sieve, preferably 53~90%, and more preferably 55~88%.

[0025] In the above-mentioned molecular sieve, the relative crystallinity of the molecular sieve is 95~115% (measured after drying and calcination at 550℃ for 2 hours), and the relative crystallinity of the molecular sieve after hydrothermal treatment with steam at 600℃ for 2 hours is 95~112%.

[0026] In the aforementioned molecular sieves, the specific surface area is 350~450 m². 2 / g, pore volume 0.31~0.6 cm³ 3 / g, microporous specific surface area is 50~200 m² 2 / g, mesoporous specific surface area is 165~400 m² 2 / g; preferably, the specific surface area is 364~440m². 2 / g, pore volume 0.34~0.57 cm³ 3 / g, with a microporous specific surface area of ​​80~180 m² 2 / g, mesoporous specific surface area is 182~363 m² 2 / g.

[0027] The aforementioned molecular sieves are used in heavy oil catalytic cracking reactions.

[0028] Compared with existing technologies, the present invention provides a method for preparing and applying ZSM-5 molecular sieves, which has the following advantages:

[0029] The ZSM-5 molecular sieve synthesized by the method of this invention possesses both the acidic properties of a microporous structure that can be tunably modified and the macroporous characteristics of a mesoporous structure. The mesoporous channels are concentrated and their relative content with the micropores can be controlled. At the same time, it has high crystallinity, strong thermal stability and hydrothermal stability, making it an excellent adsorbent or catalyst material with broader application prospects in the field of shape-selective catalysis. Furthermore, it further enhances the application performance of ZSM-5 molecular sieve in petrochemical, fine chemical, environmental protection, electrochemistry and other fields. Attached Figure Description

[0030] Figure 1 The image shows the XRD pattern of the synthesized product in Example 1 of this invention.

[0031] Figure 2 This is a diagram showing the physical adsorption of nitrogen in the synthesized product of Example 1 of the present invention. Detailed Implementation

[0032] The analytical methods of this invention are as follows: specific surface area and pore volume were determined by nitrogen physical adsorption, and the relative crystallinity of the molecular sieve was determined by X-ray powder diffraction (XRD). Specifically, the sum of the heights of five diffraction peaks at 2θ values ​​of ~8.0°, 8.9°, 23.4°, 23.8°, and 24.1° in the XRD pattern of the ZSM-5 molecular sieve synthesized in Comparative Example 1 was taken as 100% crystallinity, and the relative crystallinity of other samples was obtained by comparison with this sum.

[0033] To better illustrate the present invention, further explanation is provided below with reference to embodiments and comparative examples. However, the scope of the present invention is not limited to these embodiments, and unless otherwise specified, all percentages in the following embodiments and comparative examples refer to mass percentages.

[0034] Example 1

[0035] (1) Preparation of mesoporous silicon source

[0036] Add 25 g of water glass (SiO2 mass fraction 27 wt%) to 125 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 1 hour, in which SiO2 and C 18 The TMACl molar ratio was 1:0.08; the pH of the solution was adjusted to 2 with hydrochloric acid, and then heated in a 50°C water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550°C to obtain amorphous mesoporous silica with a specific surface area of ​​1028 m². 2 / g, pore volume 1.14 cm³ 3 / g, with a pore size of 2~10 nm.

[0037] (2) Preparation of microporous ZSM-5 molecular sieves:

[0038] a) Dissolve 13.45 g of concentrated ammonia (mass fraction of 26 wt%) in 40 g of deionized water, add 6.0 g of the mesoporous silica source prepared in (1), and stir in a 40 ℃ water bath for 3 hours;

[0039] b) Based on a total molar ratio of SiO2 in the silicon source : Al2O3 in the aluminum source : TPAOH (tetrapropylammonium hydroxide) : H2O = 1 : 0.0125 : 0.2 : 30, aluminum sulfate and tetrapropylammonium hydroxide were dissolved sequentially in the remaining water. The silicon source dispersion obtained in a) was then added to obtain the final gel. After crystallization at 180 °C for 24 hours, the gel was filtered, washed, dried, and calcined. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. Its XRD pattern is shown below. Figure 1 Similarly, the nitrogen physical adsorption curve is as follows: Figure 2 As shown, the specific properties are shown in Table 1.

[0040] Example 2

[0041] (1) Preparation of mesoporous silicon source

[0042] Add 25 g of water glass (SiO2 mass fraction 27 wt%) to 125 g of deionized water, stir to disperse evenly, then add octadecyltrimethylammonium chloride and stir for 2 hours. The SiO2 and C... 18 The TMACl molar ratio was 1:0.08; the pH of the solution was adjusted to 2 with hydrochloric acid, and then heated in a 70 ℃ water bath for 3 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550 ℃ to obtain amorphous mesoporous silica with a specific surface area of ​​964 m². 2 / g, pore volume is 1.01cm³ 3 / g, with a pore size of 2`10 nm.

[0043] (2) Preparation of microporous ZSM-5 molecular sieves:

[0044] a) Dissolve 4.71 g of concentrated ammonia (mass fraction of 26 wt%) in 30 g of deionized water, add 6.0 g of the mesoporous silica source prepared in (1), and stir in a 35 ℃ water bath for 6 hours;

[0045] b) Based on a total molar ratio of SiO2 in the silicon source : Al2O3 in the aluminum source : TPAOH : H2O = 1 : 0.04 : 0.15 : 25, aluminum sulfate and tetrapropylammonium hydroxide were sequentially dissolved in the remaining water. The silicon source dispersion obtained in a) was then added to prepare the final gel. After crystallization at 160 °C for 24 hours, the gel was filtered, washed, dried, and calcined. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. Its XRD pattern is shown below. Figure 1 Similarly, the nitrogen physical adsorption curve is as follows: Figure 2 As shown, the specific properties are shown in Table 1.

[0046] Example 3

[0047] (1) Preparation of mesoporous silicon source

[0048] Add 25 g of water glass (SiO2 mass fraction 27 wt%) to 600 g of deionized water, stir to disperse evenly, then add octadecyltrimethylammonium chloride and stir for 0.5 hours. The SiO2 and C... 18 The TMACl molar ratio was 1:0.2; the pH of the solution was adjusted to 3 with hydrochloric acid, and then heated in a 50 ℃ water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550 ℃ to obtain amorphous mesoporous silica with a specific surface area of ​​1164 m². 2 / g, pore volume 1.18 cm³ 3 / g, with a pore size of 2~10 nm.

[0049] (2) Preparation of microporous ZSM-5 molecular sieves:

[0050] a) Dissolve 6.73 g of concentrated ammonia (mass fraction of 26 wt%) in deionized water, add 6.0 g of the mesoporous silica source prepared in (1), and stir in a 40 ℃ water bath for 4 hours;

[0051] b) Based on a total molar ratio of SiO2 in the silicon source : Al2O3 in the aluminum source : TPAOH : H2O = 1 : 0.004 : 0.40 : 50, aluminum sulfate and tetrapropylammonium hydroxide were dissolved sequentially in the remaining water. The silicon source dispersion obtained in a) was then added to prepare the final gel. After crystallization at 160 °C for 32 hours, the gel was filtered, washed, dried, and calcined. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. Its XRD pattern is shown below. Figure 1 Similarly, the nitrogen physical adsorption curve is as follows: Figure 2 As shown, the specific properties are shown in Table 1.

[0052] Example 4

[0053] (1) Preparation of mesoporous silicon source

[0054] Add 25 g of water glass (SiO2 mass fraction 27 wt%) to 400 g of deionized water, stir to disperse evenly, then add octadecyltrimethylammonium chloride and stir for 2 hours. The SiO2 and C... 18 The TMACl molar ratio was 1:0.15; the pH of the solution was adjusted to 4 with hydrochloric acid, and then heated in a 40 ℃ water bath for 6 hours; after heating, the solution was filtered, washed, dried, and calcined at 550 ℃ to obtain amorphous mesoporous silica with a specific surface area of ​​1122 m². 2 / g, pore volume 0.99 cm³ 3 / g, with a pore size of 2~10 nm.

[0055] (2) Preparation of microporous ZSM-5 molecular sieves:

[0056] a) Dissolve 13.45 g of concentrated ammonia (mass fraction of 26 wt%) in 40 g of deionized water, add 6.0 g of the mesoporous silica source prepared in (1), and stir in a 30 ℃ water bath for 8 hours;

[0057] b) Based on a total molar ratio of SiO2 in the silicon source : Al2O3 in the aluminum source : TPAOH : H2O = 1 : 0.004 : 0.40 : 50, aluminum sulfate and tetrapropylammonium hydroxide were sequentially dissolved in the remaining water. The silicon source dispersion obtained in a) was then added to obtain the final gel. After crystallization at 180 °C for 10 hours, the gel was filtered, washed, dried, and calcined. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. Its XRD pattern is shown below. Figure 1 Similarly, the nitrogen physical adsorption curve is as follows: Figure 2 As shown, the specific properties are shown in Table 1.

[0058] Example 5

[0059] (2) Preparation of mesoporous silicon source

[0060] Add 25 g of water glass (SiO2 mass fraction 27 wt%) to 125 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 1 hour, in which SiO2 and C 18 The TMACl molar ratio was 1:0.08; the pH of the solution was adjusted to 2 with hydrochloric acid, and then heated in a 50°C water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550°C to obtain amorphous mesoporous silica with a specific surface area of ​​1028 m². 2 / g, pore volume 1.14 cm³ 3 / g, with a pore size of 2-10 nm.

[0061] (2) Preparation of microporous ZSM-5 molecular sieves:

[0062] a) Dissolve 13.45 g of concentrated ammonia (mass fraction of 26 wt%) in 40 g of deionized water, add 6.0 g of the mesoporous silica source prepared in (1), and stir in a 30 ℃ water bath for 1 hour;

[0063] b) Based on a total molar ratio of SiO2 in the silicon source : Al2O3 in the aluminum source : TPAOH : H2O = 1 : 0.0125 : 0.2 : 30, aluminum sulfate and tetrapropylammonium hydroxide were sequentially dissolved in the remaining water. The silicon source dispersion obtained in a) was then added to prepare the final gel. After crystallization at 180 °C for 24 hours, the gel was filtered, washed, dried, and calcined. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. Its XRD pattern is shown below. Figure 1 Similarly, the nitrogen physical adsorption curve is as follows: Figure 2As shown, the specific properties are shown in Table 1.

[0064] Comparative Example 1 (Refer to CN103071522A)

[0065] First, 2 g of sodium aluminate was dissolved in 200 mL of 20-25% TPAOH solution. After complete dissolution, 670 g of deionized water and 73 g of fumed silica were added. After stirring for 2 hours, the mixture was transferred to a polytetrafluoroethylene-lined reactor and aged at 60°C for 24 hours. Then, the second template agent, hexadecyltrimethylammonium bromide (CTAB), was added to the mixture and stirred until completely dissolved. After homogeneous crystallization at 150°C for 48 hours, the mixture was filtered, washed, and dried at 110°C for 24 hours. Finally, it was calcined at 550°C for 10 hours to obtain hierarchical porous ZSM-5 molecular sieve. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600°C for 2 hours, its hydrothermal stability was measured. The specific properties are shown in Table 1.

[0066] Comparative Example 2:

[0067] (1) Preparation of mesoporous silicon source

[0068] Add 25 g of water glass (SiO2 mass fraction 27 wt%) to 125 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 1 hour, in which SiO2 and C 18 The TMACl molar ratio was 1:0.08; the pH of the solution was adjusted to 2 with hydrochloric acid, and then heated in a 50°C water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550°C to obtain amorphous mesoporous silica.

[0069] (2) Preparation of microporous ZSM-5 molecular sieves:

[0070] a) Add 6.0 g of the mesoporous silicon source obtained in (1) to 40 g of deionized water and stir in a 40 ℃ water bath for 3 hours;

[0071] b) Based on a total molar ratio of SiO2 in silicon source : Al2O3 in aluminum source : TPAOH (tetrapropylammonium hydroxide) : H2O = 1 : 0.0125 : 0.2 : 30, aluminum sulfate and tetrapropylammonium hydroxide were dissolved sequentially in the remaining water, and then the silicon source dispersion obtained in a) was added to obtain the final gel. After crystallization at 180 °C for 24 hours, the gel was filtered, washed, dried, and calcined. The relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, the hydrothermal stability was measured. The specific properties are shown in Table 1.

[0072] Comparative Example 3

[0073] A gel with a total molar ratio of SiO2 from silicon source : Al2O3 from aluminum source : NaOH : TPAOH : H2O = 1 : 0.016 : 0.35 : 0.1 : 30 was prepared by mixing water glass, aluminum sulfate, tetrapropylammonium hydroxide, sodium hydroxide and water. After heating at 180 °C for 24 hours, the product was obtained. After filtration, washing, drying and calcination, its relative crystallinity was measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. The specific properties are shown in Table 1.

[0074] Table 1

[0075] Specific surface area, m 2 / g]] <![CDATA[Micropore surface area, m 2 / g]]> <![CDATA[Mesoporous surface area, m 2 / g]]> <![CDATA[Pore volume, cm 3 / g]]> Mesoporous content with pore size of 2~6 nm, % Relative density, % Relative crystallinity after hydrothermal treatment, % Example 1 438 123 315 0.52 85 105 103 Example 2 401 107 294 0.44 61 104 103 Example 3 413 114 299 0.47 77 113 111 Example 4 445 127 318 0.55 86 102 99 Example 5 357 156 201 0.37 56 101 102 Comparative Example 1 418 113 305 0.57 22 100 95 Comparative Example 2 126 68 58 0.11 <![CDATA[- a ]]> <![CDATA[- a ]]> <![CDATA[- a ]]> Comparative Example 3 214 171 43 0.16 6 101 99

[0076] a The products generated under these conditions are mainly a mixture of other molecular sieves and a large amount of amorphous silica, therefore this property cannot be analyzed.

[0077] As shown in Table 1, the preparation method of this invention can produce ZSM-5 molecular sieves with microporous composite structures through a simple synthesis process. It uses relatively little surfactant and microporous template agent, and the cost is low. The resulting microporous composite ZSM-5 molecular sieve exhibits high crystallinity, large specific surface area and pore volume, high mesopore content and concentrated size distribution, good thermal and hydrothermal stability, and broad application prospects.

[0078] The heavy oil catalytic cracking performance of ZSM-5 molecular sieve samples was evaluated in a fixed-bed microreactor. Molecular sieve tablets were crushed into 20–40 mesh particles and then loaded into the reactor. The reaction temperature was 650 °C and the gas hourly space velocity (GHSV) was 1400 h⁻¹. -1 Under normal pressure conditions, the properties of the feedstock oil are shown in Table 2.

[0079] The reaction results of Comparative Example 1, Comparative Example 3 and Example 1 in the heavy oil catalytic cracking reaction are as follows:

[0080] Comparative Example 1: Activity: 78%; Ethylene yield: 1.2%; Propylene yield: 20.4%; Diene yield: 21.6%.

[0081] Comparative Example 3: Activity: 76%; Ethylene yield: 1.1%; Propylene yield: 12.3%; Diene yield: 13.4%.

[0082] Example 1: Activity: 79%; Ethylene yield: 3.8%; Propylene yield: 22.7%; Diene yield: 26.5%.

[0083] Table 2

[0084] project properties of crude oil <![CDATA[Density (20 °C), g / cm 3 > 0.9082 <![CDATA[Viscosity (40 °C), mm 2 / s]]> 0.210 H / C 1.80 Saturated hydrocarbons (%) 60.1 Aromatic hydrocarbons (%) 28.7 Asphalt content (%) 11.2

Claims

1. A method for preparing ZSM-5 molecular sieve, characterized in that: A silicon source, an aluminum source, a microporous template agent, and water are mixed to form a gel. The gel is then crystallized at 150–200 °C for 6–36 hours. After filtration, washing, drying, and calcination, ZSM-5 molecular sieve is obtained. The silicon source is amorphous silica treated with an alkali. The alkali treatment is an inorganic alkali treatment, which involves adding the prepared or selected amorphous silica to an alkaline solution and heating and stirring. The pore diameter of the amorphous silica is 2–10 nm. The molar ratio of silicon source (SiO2): aluminum source (Al2O3): template agent: H2O in the gel is 1:(0.003–0.05):(0.05–0.50):(20–60).

2. The method according to claim 1, characterized in that: The molar ratio of silicon source (SiO2): aluminum source (Al2O3): template agent: H2O in the gel is 1:(0.005~0.05):(0.08~0.40):(25~50).

3. The method according to claim 1, characterized in that: ZSM-5 molecular sieve was obtained by crystallizing the gel at 160~180 ℃ for 8~32 hours, followed by filtration, washing, drying and calcination.

4. The method according to claim 1, characterized in that: The amorphous silica has a specific surface area of ​​600~1300 m². 2 / g; pore volume is 0.6~1.3 cm³ 3 / g.

5. The method according to claim 4, characterized in that: The amorphous silica has a specific surface area of ​​700~1200 m². 2 / g; pore volume is 0.7~1.2 cm³ 3 / g.

6. The method according to claim 4 or 5, characterized in that: The preparation process of the amorphous silica is as follows: the silicon source is added to deionized water and dispersed evenly, and then a surfactant is added and stirred; after adjusting the pH of the solution to 1-5, it is heated in a water bath for a period of time. Amorphous silica was obtained by filtering, washing, drying, and calcining.

7. The method according to claim 6, characterized in that: The preparation process of the amorphous silica is as follows: the silicon source is added to deionized water and dispersed evenly, and then a surfactant is added and stirred; after adjusting the pH of the solution to 1.5~4, it is heated in a water bath for a period of time. Amorphous silica was obtained by filtering, washing, drying, and calcining.

8. The method according to claim 1, characterized in that: The inorganic base is one or more of ammonia, sodium hydroxide, and potassium hydroxide.

9. The method according to claim 8, characterized in that: The inorganic base is ammonia.

10. The method according to claim 1, characterized in that: The alkali treatment heating and stirring time is 0.5~12 hours; the heating temperature is 25~60 ℃.

11. The method according to claim 10, characterized in that: The alkali treatment heating and stirring time is 2-8 hours; the heating temperature is 30-50℃.

12. The method according to claim 1, characterized in that: The alkaline treatment uses OH - The molar ratio of inorganic alkali to amorphous silica (based on SiO2) is 0.30 to 1.

12.

13. The method according to claim 12, characterized in that: The alkaline treatment uses OH - The molar ratio of inorganic alkali to amorphous silica (based on SiO2) is 0.35 to 1.

0.

14. The method according to claim 1, characterized in that: The drying temperature is 80~120 ℃, the drying time is 4~12 hours, the calcination temperature is 500~600 ℃, and the calcination time is 2~6 hours.

15. A ZSM-5 molecular sieve prepared by any one of claims 1 to 14, wherein the mesopore volume with a pore size of 2 to 6 nm accounts for 50 to 92% of the total pore volume of the molecular sieve.

16. The molecular sieve according to claim 15, characterized in that: In the molecular sieve, mesopores with a pore size of 2-6 nm account for 53-90% of the total pore volume.

17. The molecular sieve according to claim 15, characterized in that: In the molecular sieve, mesopores with a pore size of 2-6 nm account for 55-88% of the total pore volume.

18. The molecular sieve according to any one of claims 15-17, characterized in that: The relative crystallinity of the molecular sieve is 95-115%, and the relative crystallinity of the molecular sieve after being subjected to hydrothermal treatment with steam at 600 ℃ for 2 hours is 95-112%.

19. The molecular sieve according to any one of claims 15-17, characterized in that: The specific surface area of ​​the molecular sieve is 350~450 m². 2 / g, pore volume 0.31~0.6 cm³ 3 / g, microporous specific surface area is 50~200 m² 2 / g, mesoporous specific surface area is 165~400m² 2 / g.

20. The molecular sieve according to claim 19, characterized in that: The specific surface area of ​​the molecular sieve is 364~440 m². 2 / g, pore volume 0.34~0.57 cm³ 3 / g, with a microporous specific surface area of ​​80~180 m² 2 / g, mesoporous specific surface area is 182~363 m² 2 / g.

21. The molecular sieve of any one of claims 15 to 20 is used in heavy oil catalytic cracking reaction.

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