A ZSM-5 molecular sieve and its synthesis method

Abstract

The present invention discloses a ZSM-5 molecular sieve and a synthesis method thereof. The ZSM-5 molecular sieve crystal is composed of a number of cuboid small crystallites. The length of the cuboid small crystallites is 150-300 nm, the width is 50-80 nm, and the thickness is 10-50 nm. There are obvious slit-shaped pores between adjacent cuboid crystallites. The synthesis method of the ZSM-5 molecular sieve comprises the following steps: mixing an inorganic base, a silicon source, an aluminum source, a template agent and water, and performing a first-stage crystallization reaction after mixing evenly; then introducing lignosulfonate and sulfate into the reaction system for a second-stage crystallization reaction. After the second-stage crystallization reaction is completed, the ZSM-5 molecular sieve is obtained through further separation, drying and calcination. The present invention prepares a micron-sized large particle ZSM-5 molecular sieve composed of nano-sized crystals.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing molecular sieves, belonging to the field of molecular sieve synthesis, and particularly relates to a ZSM-5 molecular sieve and a method for synthesizing the same. Background Art

[0002] In the early 1970s, ZSM-5 molecular sieve was successfully developed by Mobil Corporation for the first time. It is a zeolite molecular sieve with a unique three-dimensional channel structure and acid strength distribution. Most of its pore diameters are about 0.55 nm, and it has the characteristics of high silica-alumina ratio, lipophilicity and hydrophobicity, as well as high thermal stability and catalytic activity. It is widely used in the field of petrochemical industry.

[0003] CN102951656A discloses a method for synthesizing ZSM-5 molecular sieve with uniform particles. In this method, a seed mixture solution is first prepared by a coprecipitation method. During coprecipitation, the precipitation pH value is controlled at 8-11. After precipitation, the precipitate is ground to a certain fineness by a grinding device, and then a seed mixture solution is obtained by crystallization. Then, a precipitation mixture is obtained by a coprecipitation method, a certain proportion of the seed mixture solution is added, and after crystallization, filtration, washing and calcination, ZSM-5 molecular sieve with uniform particle size is obtained.

[0004] CN106673008A discloses a hierarchical structure ZSM-5 zeolite molecular sieve, a synthesis method thereof and an application. This method first treats the silicon source. The template agent is added to water and stirred to disperse to obtain a template agent solution. Water is added to the silicon source and stirred to obtain a silicon source solution. Then, the template agent solution is dropped into the silicon source solution and stirred for 4-5 hours, aged at 40-80 °C for 6-12 hours, and then an aqueous solution containing an inorganic base or an alkali metal compound is dropped and stirred for 4-5 hours, and then aged at 40-80 °C for 6-12 hours to obtain an aged silicon source. Then, it is hydrothermal synthesis. One or more of an aluminum source, a titanium source or an iron source are dissolved in water, the pH value is adjusted, and stirred evenly until it is in a clear state to obtain solution A. Solution A is dropped into the aged silicon source solution and stirred for 1-5 hours, and hydrothermally crystallized to obtain ZSM-5 zeolite molecular sieve

[0005] CN104108724A discloses a method for synthesizing small crystal P-ZSM-5 molecular sieve from low-cost raw materials. In this invention, aluminum sulfate, concentrated sulfuric acid, sodium chloride, isopropyl alcohol, water glass, n-butylamine, ZSM-5 molecular sieve seeds and an aqueous solution containing phosphorus are mixed and stirred evenly. After aging under stirring, crystallization, filtration, drying and calcination, small crystal P-ZSM-5 molecular sieve is obtained.

[0006] CN106587100A discloses a method for synthesizing flaky ZSM-5 zeolite molecular sieve with a single small molecule organic template agent. The steps of this method are as follows: Mix water, a silicon source, an alkali source, and a template agent, or continue to mix evenly after adding an aluminum source; then place it in a reaction kettle, filter the product obtained from the crystallization reaction, and dry it to obtain the ZSM-5 zeolite molecular sieve. The template agent used in this patent is 3,5-dimethyl-N-butyl pyridinium iodide. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides a ZSM-5 molecular sieve and its preparation and synthesis method, and prepares a micron-sized large particle ZSM-5 molecular sieve composed of nanoscale crystals.

[0008] The present invention first provides a ZSM-5 molecular sieve. The ZSM-5 molecular sieve crystal is composed of several cuboid small grains. The length of the cuboid small grains is 150-300 nm, the width is 50-80 nm, and the thickness is 10-50 nm. There are obvious gap-like pores between adjacent cuboid grains.

[0009] Furthermore, the crystal size of the above ZSM-5 molecular sieve is 1-30 μm.

[0010] Furthermore, the specific surface area of the above ZSM-5 molecular sieve is 400-700 m 2 / g, and the pore volume is 0.2-0.55 cm 3 / g.

[0011] Furthermore, the above ZSM-5 molecular sieve has concentrated mesoporous channels, and the most probable pore diameter is 10-30 nm.

[0012] The present invention provides a synthesis method of a ZSM-5 molecular sieve. The synthesis method includes the following steps: Mix an inorganic base, a silicon source, an aluminum source, a template agent, and water, and carry out a first-stage crystallization reaction after mixing evenly; after the first-stage crystallization reaction is completed, cool the temperature of the reaction system to 10-30 °C, and then introduce lignosulfonate and sulfate into the reaction system for a second-stage crystallization reaction. After the second-stage crystallization reaction is completed, further obtain the ZSM-5 molecular sieve through separation, drying, and calcination.

[0013] In the above synthesis method of the ZSM-5 molecular sieve, the inorganic base can be one or several of sodium hydroxide and potassium hydroxide.

[0014] In the above synthesis method of the ZSM-5 molecular sieve, the aluminum source can be one or several of aluminum chloride, sodium aluminate, aluminum sulfate, and aluminum nitrate, and preferably aluminum chloride and / or aluminum nitrate.

[0015] In the above synthesis method of ZSM-5 molecular sieve, the silicon source can be one or more of silica gel, white carbon black, silica sol, and water glass.

[0016] In the above synthesis method of ZSM-5 molecular sieve, the template agent is at least one of n-butylamine, ethylenediamine, hexamethylenediamine, and tetrapropylammonium hydroxide, preferably at least one of n-butylamine and ethylenediamine.

[0017] In the above synthesis method of ZSM-5 molecular sieve, the control conditions of the first-stage crystallization reaction are as follows: the reaction temperature is 150-230°C, preferably 170-200°C; the reaction time is 2-15 h, preferably 5-10 h.

[0018] In the above synthesis method of ZSM-5 molecular sieve, the molar ratio of the inorganic base, silicon source, aluminum source, template agent, and water is: 0.5-4 inorganic base: 30-120 SiO2: Al2O3: 800-2000 H2O: 5-20 template agent, preferably 1-3 inorganic base: 40-100 SiO2: Al2O3: 1000-1700 H2O: 7-16 template agent.

[0019] In the above synthesis method of ZSM-5 molecular sieve, the mass ratio of the lignosulfonate to the silicon source is 0.03-0.15:1, preferably 0.05-0.1:1.

[0020] In the above synthesis method of ZSM-5 molecular sieve, the lignosulfonate can be selected from sodium lignosulfonate and / or potassium lignosulfonate, preferably sodium lignosulfonate.

[0021] In the above synthesis method of ZSM-5 molecular sieve, the sulfate can be at least one of sodium sulfate, potassium sulfate, magnesium sulfate, iron sulfate, and copper sulfate, preferably sodium sulfate and / or potassium sulfate.

[0022] In the above synthesis method of ZSM-5 molecular sieve, the mass ratio of the sulfate to the silicon source is 0.03-0.15:1, preferably 0.05-0.1:1.

[0023] In the above synthesis method of ZSM-5 molecular sieve, the control conditions of the second-stage crystallization reaction are as follows: the reaction temperature is 130-180°C, preferably 140-180°C; the reaction time is 15-55 h, preferably 20-60 h.

[0024] In the above synthesis method of ZSM-5 molecular sieve, the reaction temperature of the second-stage crystallization reaction is lower than that of the first-stage crystallization reaction. Specifically, the reaction temperature of the second-stage crystallization reaction is 5-25°C lower than that of the first-stage crystallization reaction, preferably 10-20°C lower.

[0025] In the above synthesis method of ZSM-5 molecular sieve, the separation can be carried out by filtration, usually multiple filtrations, which can be 1 to 10 times.

[0026] In the above synthesis method of ZSM-5 molecular sieve, the drying is carried out at 100 - 150 °C for 1 - 10 h.

[0027] In the above synthesis method of ZSM-5 molecular sieve, the calcination is carried out at a high temperature of 400 - 600 °C for 1 - 10 h, and the calcination needs to be carried out in air or oxygen.

[0028] The third aspect of the present invention provides a ZSM-5 molecular sieve obtained by the above synthesis method.

[0029] Furthermore, the above ZSM-5 molecular sieve crystal is composed of several cuboid small grains. The length of the cuboid small grains is 150 - 300 nm, the width is 50 - 80 nm, and the thickness is 10 - 50 nm. There are obvious gap-like pores between adjacent cuboid grains.

[0030] Furthermore, the crystal size of the above ZSM-5 molecular sieve is 1 - 30 μm.

[0031] Furthermore, the specific surface area of the above ZSM-5 molecular sieve is 400 - 700 m 2 / g, and the pore volume is 0.2 - 0.55 cm 3 / g.

[0032] Furthermore, the above ZSM-5 molecular sieve has concentrated mesoporous channels, and the most probable pore diameter is 10 - 30 nm.

[0033] The ZSM-5 molecular sieve provided by the present invention has good macromolecular substance transport ability, can be used as an acidic component of a catalyst, or an adsorption separation agent; it can be widely used in the petrochemical industry or other chemical industry production processes.

[0034] The ZSM-5 molecular sieve of the present invention has unique physical and chemical characteristics. Compared with the traditional bulk ZSM-5 molecular sieve, there are huge differences in the diffusion pathways of substances in the pores of the two materials during the adsorption or catalytic reaction process. Therefore, the ZSM-5 molecular sieve of the present invention has different properties and characteristics from the traditional ZSM-5 molecular sieve.

[0035] Compared with the prior art, the ZSM-5 molecular sieve and its synthesis method provided by the present invention have the following advantages:

[0036] In the synthesis process of ZSM-5 molecular sieve, the nucleation process in the initial stage of molecular sieve synthesis is the control step, which determines the final crystal structure of the molecular sieve. The raw materials for molecular sieve synthesis generally include alkali, silicon source, aluminum source, water and template agent. In order to regulate the properties of molecular sieve crystals, various additives are usually added during the synthesis process to modulate the properties of the molecular sieve. However, when additives are introduced into the molecular sieve synthesis system, the additives will affect the growth of molecular sieve crystal nuclei. Especially when the introduced additives do not match the synthesis system, it will hinder the nucleation of the molecular sieve and lead to the inability to synthesize the target product. Lignosulfonate is an adverse factor for the synthesis of ZSM-5 molecular sieve. If lignosulfonate is added to the synthesis system in the starting raw materials, it will cause the inability to synthesize ZSM-5 molecular sieve crystals. The ZSM-5 molecular sieve synthesis method of the present invention synthesizes ZSM-5 molecular sieve by a two-stage crystallization method. The first stage is the molecular sieve nucleation process; in the second stage, additives lignosulfonate and sulfate are added, and by combining the regulation of the two-stage crystallization conditions, the lignosulfonate is combined on certain crystal faces of the molecular sieve, thus controlling the morphology of the ZSM-5 molecular sieve crystals. The introduction of sulfate regulates the electrical properties of the reaction system and further promotes the degree of combination of lignosulfonate with the molecular sieve crystals. Moreover, adding lignosulfonate in the second stage after nucleation completion can avoid its influence on the molecular sieve nucleation process and avoid the inability to synthesize ZSM-5 molecular sieve products. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 SEM photograph of the ZSM-5 molecular sieve obtained in Example 1 of the present invention.

[0038] Figure 2 Pore size distribution diagram of the ZSM-5 molecular sieve obtained in Example 1 of the present invention.

[0039] Figure 3 SEM photograph of the ZSM-5 molecular sieve obtained in Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The technical solutions and effects of the present invention will be further described below in conjunction with embodiments, but are not limited to the following embodiments. In the present invention, wt% is the mass fraction.

[0041] The pore structure parameters such as specific surface area of the samples in the present invention are measured by the low-temperature nitrogen adsorption method, and a ASAP2400 type physical adsorption instrument produced by Micromeritics Instrument Corporation of the United States is used for test characterization. Before measurement, the samples are vacuum-treated at 300 °C for more than 4 h. Among them, the total specific surface area is calculated according to the BET isotherm equation. The pore size distribution is calculated by the BJH method.

[0042] In this invention, the crystal structure of the sample was characterized by an X-ray diffractometer, using a Rigaku D / max2500 X-ray diffractometer, with a Cu target, Kα radiation source, graphite monochromator, tube voltage of 40 kV, tube current of 80 mA, scanning range of 5° to 40°, step size of 0.1°, and scanning speed of 1 ° / min.

[0043] In this invention, the microscopic morphology of the sample was characterized by a scanning electron microscope: using a JSM-6301F scanning electron microscope (equipped with Oxford EDS) from JEOL Ltd., Japan, working voltage: 20 kV, working distance: 15 mm, resolution: 1.5 nm.

[0044] Example 1

[0045] 0.2 g of sodium hydroxide, 12.6 g of silica white, 1.0 g of aluminum chloride, 2.3 g of n-butylamine, and 85 g of distilled water were mixed evenly and reacted at 180 °C for 8 h; after the reaction ended, the temperature was lowered to 25 °C, then 0.88 g of sodium lignosulfonate and 0.88 g of potassium sulfate were added, and the reaction was carried out at 160 °C for 55 h; then the obtained sample was filtered 5 times, and then placed in an oven and dried at 130 °C for 10 h, and calcined at 600 °C in a high-temperature furnace for 3 h. The obtained sample was numbered M1, and the properties of the sample are shown in Table 1. Its SEM photograph is shown in Figure 1 From the SEM photograph, it can be seen that the crystal morphology of the molecular sieve is granular on the micron scale, about 5 μm; and it is composed of an orderly accumulation of regular sheet-like cuboid small crystals. The length of the cuboid crystals is about 100 - 200 nm, the width is about 50 nm, and the thickness is about 20 nm. There are obvious gaps between the cuboid crystals.

[0046] Example 2

[0047] 0.15 g of sodium hydroxide, 22.5 g of silica gel, 1.0 g of aluminum chloride, 4.4 g of n-butylamine, and 114.7 g of distilled water were mixed evenly and reacted at 170 °C for 10 h; after the reaction ended, the temperature was lowered to 25 °C, then 1.13 g of sodium lignosulfonate and 1.13 g of sodium sulfate were added, and the reaction was carried out at 150 °C for 20 h; then the obtained sample was filtered 5 times, and then placed in an oven and dried at 130 °C for 10 h, and calcined at 600 °C in a high-temperature furnace for 3 h. The obtained sample was numbered M2, and the properties of the sample are shown in Table 1.

[0048] Example 3

[0049] Mix 0.45 g of sodium hydroxide, 9 g of silica white, 1.0 g of aluminum chloride, 1.9 g of n-butylamine, and 67.5 g of distilled water evenly, and react at 200 °C for 5 h; after the reaction is completed, lower the temperature to 25 °C, then add 0.9 g of sodium lignosulfonate and 0.9 g of sodium sulfate, and react at 180 °C for 60 h; then filter the obtained sample 5 times, then place it in an oven and dry at 130 °C for 10 h, and calcine at 600 °C in a high-temperature furnace for 3 h. The obtained sample is numbered M3, and the sample properties are shown in Table 1.

[0050] Example 4

[0051] Mix 0.45 g of potassium hydroxide, 15 g of silica white, 1.8 g of aluminum nitrate nonahydrate, 2.5 g of ethylenediamine, and 70 g of distilled water evenly, and react at 185 °C for 5 h; after the reaction is completed, lower the temperature to 25 °C, then add 1.05 g of sodium lignosulfonate and 1.05 g of potassium sulfate, and react at 160 °C for 50 h; then filter the obtained sample 5 times, then place it in an oven and dry at 130 °C for 10 h, and calcine at 600 °C in a high-temperature furnace for 3 h. The obtained sample is numbered M3, and the sample properties are shown in Table 1.

[0052] Example 5

[0053] Mix 0.52 g of sodium hydroxide, 10.5 g of silica gel, 2.1 g of aluminum nitrate nonahydrate, 3.5 g of ethylenediamine, and 90 g of distilled water evenly, and react at 195 °C for 7 h; after the reaction is completed, lower the temperature to 25 °C, then add 0.74 g of sodium lignosulfonate and 0.74 g of potassium sulfate, and react at 175 °C for 43 h; then filter the obtained sample 5 times, then place it in an oven and dry at 130 °C for 10 h, and calcine at 600 °C in a high-temperature furnace for 3 h. The obtained sample is numbered M3, and the sample properties are shown in Table 1.

[0054] Comparative Example 1

[0055] Mix 0.2 g of sodium hydroxide, 12.6 g of silica white, 1.0 g of aluminum chloride, 2.3 g of n-butylamine, 0.88 g of sodium lignosulfonate, 0.88 g of sodium sulfate, and 85 g of distilled water evenly, and react at 180 °C for 8 h; after the reaction is completed, lower the temperature to 25 °C, then react at 160 °C for 55 h; then filter the obtained sample 5 times, then place it in an oven and dry at 130 °C for 10 h, and calcine at 600 °C in a high-temperature furnace for 3 h. The obtained sample is numbered M6, and the sample properties are shown in Table 1. The obtained sample is an amorphous substance, indicating that directly adding lignin will affect the nucleation of molecular sieves and prevent the raw materials from crystallizing.

[0056] Comparative Example 2

[0057] Mix 0.2 g of sodium hydroxide, 12.6 g of silica white, 1.0 g of aluminum chloride, 2.3 g of n-butylamine, and 85 g of distilled water evenly, and react at 180 °C for 63 h; then filter the obtained sample 5 times, and then place it in an oven at 130 °C for drying for 10 h, and calcine it in a high-temperature furnace at 600 °C for 3 h. The obtained sample is numbered M7. The properties of the sample are shown in Table 1, and its SEM photograph is shown in Figure 2 . It can be seen from the SEM photograph that the morphology of the molecular sieve obtained by the conventional method is large-particle single crystals at the micron scale.

[0058] Comparative Example 3

[0059] Mix 0.2 g of sodium hydroxide, 12.6 g of silica white, 1.0 g of aluminum chloride, 2.3 g of n-butylamine, and 85 g of distilled water evenly, and react at 180 °C for 8 h; after the reaction is completed, lower the temperature to 25 °C, and then add 0.88 g of sodium lignosulfonate and react at 160 °C for 55 h; then filter the obtained sample 5 times, and then place it in an oven at 130 °C for drying for 10 h, and calcine it in a high-temperature furnace at 600 °C for 3 h. The obtained sample is numbered M8, and the morphology of the molecular sieve obtained is large-particle single crystals at the micron scale.

[0060] Comparative Example 4

[0061] Mix 0.2 g of sodium hydroxide, 12.6 g of silica white, 1.0 g of aluminum chloride, 2.3 g of n-butylamine, and 85 g of distilled water evenly, and react at 180 °C for 8 h; after the reaction is completed, lower the temperature to 25 °C, and then add 0.88 g of potassium sulfate and react at 160 °C for 55 h; then filter the obtained sample 5 times, and then place it in an oven at 130 °C for drying for 10 h, and calcine it in a high-temperature furnace at 600 °C for 3 h. The obtained sample is numbered M9, and the morphology of the molecular sieve obtained is large-particle single crystals at the micron scale.

[0062] Table 1 Properties of Samples in Examples and Comparative Examples

[0063]

[0064] Note: In this invention, the crystallinity of the molecular sieve in Example 1 is taken as 100%, and the crystallinity of all samples is obtained by comparing with the crystallinity of this sample.

[0065] The pore structure of the molecular sieve material of this invention is characterized by N2 adsorption-desorption, and the crystal particle size and state are characterized by scanning electron microscopy.

Claims

1. A method for synthesizing a ZSM-5 molecular sieve, the method comprising the following steps: mixing an inorganic base, a silicon source, an aluminum source, a template, and water, and conducting a first-stage crystallization reaction after uniform mixing; cooling the reaction system to 10-30° C. after the first-stage crystallization reaction is completed, then introducing lignin sulfonate and sulfate into the reaction system to conduct a second-stage crystallization reaction; after the second-stage crystallization reaction is completed, further separation, drying, and calcination are performed to obtain the ZSM-5 molecular sieve; the reaction temperature of the second-stage crystallization reaction is 5-25° C. lower than the reaction temperature of the first-stage crystallization reaction.

2. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, wherein: The inorganic base is one or more of sodium hydroxide and potassium hydroxide.

3. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, wherein: The aluminum source is one or more of aluminum chloride, sodium aluminate, aluminum sulfate, and aluminum nitrate.

4. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 3, characterized in that: The aluminum source is aluminum chloride and / or aluminum nitrate.

5. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, wherein: The silicon source is one or more of silica gel, white carbon black, silica sol and water glass.

6. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, wherein: The template agent is at least one of n-butylamine, ethylenediamine, hexamethylenediamine and tetrapropylammonium hydroxide.

7. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 6, characterized in that: The template agent is at least one of n-butylamine and ethylenediamine.

8. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, wherein: The control conditions of the first-stage crystallization reaction are as follows: reaction temperature is 150-230°C, and reaction time is 2-15h.

9. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 8, characterized in that: The control conditions of the first-stage crystallization reaction are as follows: reaction temperature is 170-200°C, and reaction time is 5-10h.

10. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The molar ratio of the inorganic base, silicon source, aluminum source, template agent and water is 0.5-4 inorganic base: 30-120 SiO2: A12O3: 800-2000 H2O: 5-20 template agent.

11. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 10, characterized in that: The molar ratio of the inorganic base, silicon source, aluminum source, template and water is 1-3 inorganic base: 40-100 SiO2: A12O3: 1000-1700 H2O: 7-16 template.

12. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The mass ratio of lignin sulfonate to silicon source is 0.03-0.15:

1.

13. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 12, characterized in that: The mass ratio of lignin sulfonate to silicon source is 0.05-0.1:

1.

14. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The lignin sulfonate is selected from sodium lignin sulfonate and / or potassium lignin sulfonate.

15. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 14, characterized in that: The lignin sulfonate is sodium lignin sulfonate.

16. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The sulfate is at least one of sodium sulfate, potassium sulfate, magnesium sulfate, iron sulfate, and copper sulfate.

17. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 16, characterized in that: The sulfate is sodium sulfate and / or potassium sulfate.

18. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The mass ratio of sulfate to silicon source is 0.03-0.15:

1.

19. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 8, characterized in that: The mass ratio of sulfate to silicon source is 0.05-0.1:

1.

20. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The control conditions of the second-stage crystallization reaction are as follows: reaction temperature is 130-180°C, and reaction time is 15-55h.

21. The method for synthesizing the ZSM-5 molecular sieve according to claim 1 or 20, characterized in that: The control conditions of the second-stage crystallization reaction are as follows: reaction temperature is 140-180°C, and reaction time is 20-60h.

22. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The reaction temperature of the second-stage crystallization reaction is 10 to 20° C. lower than that of the first-stage crystallization reaction.

23. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The drying is carried out at 100-150°C for 1-10 hours.

24. The method for synthesizing the ZSM-5 molecular sieve according to claim 1, characterized in that: The calcination is carried out at a high temperature of 400 to 600° C. for 1 to 10 hours.

25. A ZSM-5 molecular sieve obtained by the synthesis method according to any one of claims 1 to 24.

26. The ZSM-5 molecular sieve according to claim 25, characterized in that: The ZSM-5 molecular sieve crystal is composed of a number of small rectangular crystals with a length of 150 to 300 nm, a width of 50 to 80 nm, and a thickness of 10 to 50 nm. There are obvious slit-like channels between adjacent rectangular crystals.

27. The ZSM-5 molecular sieve according to claim 25, characterized in that: The crystal size of ZSM-5 molecular sieve is 1 to 30 μm.

28. The ZSM-5 molecular sieve according to claim 25, characterized in that: The specific surface area of ZSM-5 molecular sieve is 400~700m 2 / g, pore volume of 0.2~0.55cm 3 / g.

29. The ZSM-5 molecular sieve according to claim 25, characterized in that: ZSM-5 molecular sieve has concentrated mesoporous channels with a maximum pore diameter of 10 to 30 nm.

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