Method for synthesizing beta molecular sieve without template agent, product and application of product

Abstract

The invention discloses a method for synthesizing a beta molecular sieve without a template agent, which is characterized in that one or more of silicon-containing compounds capable of reacting with an aluminum source to form gel are used as a first silicon source, and solid silica gel is used as a second silicon source; the first silicon source and the aluminum source react in an alkaline state to form viscous gel, then the second silicon source and the seed crystal are added into the viscous gel to form a synthetic mixture, and the synthetic mixture is subjected to hydrothermal crystallization to obtain the beta molecular sieve. The template-agent-free synthesis method is simple in step and suitable for actual industrial production.

Description

Technical Field

[0001] The present invention relates to molecular sieve products, preparation methods and applications, and further to the preparation of beta molecular sieves, the obtained beta molecular sieves and applications of the beta molecular sieves in alkylation reactions and hydrocarbon cracking reactions. Background Art

[0002] β molecular sieve has a three-dimensional twelve-membered ring channel structure and was first synthesized by Mobil Corporation in the United States in 1967 (US3,308,069). Due to its unique topological structure and good thermal and hydrothermal stability, β molecular sieve exhibits excellent catalytic performance in reactions such as hydrocracking, hydroisomerization, hydrocarbon cracking, and alkylation, and has now been industrialized.

[0003] Traditionally, β molecular sieves are synthesized in the presence of organic templates, but their high synthesis cost and pollution during production and post-processing limit their application prospects and scope.

[0004] CN101249968A discloses for the first time a method for synthesizing β molecular sieve without the participation of an organic template agent. The method is to prepare an initial gel by mixing a silicon source, an aluminum source, a sodium source, and water, then add a β molecular sieve seed, and perform a hydrothermal reaction to finally obtain a β molecular sieve product. Since an organic template agent is not added to the synthesis system of the synthesis method, it is difficult to maintain the stability of the reaction system only by the structural guidance of the seed, so the phase region of the synthetic β molecular sieve is very narrow, the actual reaction conditions are difficult to control, and it is easy to produce impure crystals. If you want to achieve an ideal gel state, the preferred silicon source is extremely low-density white carbon black and liquid silicon source silica sol. The problem is that white carbon black has difficulties in storage, transportation, and feeding process in industry, and silica sol also has a low silicon concentration and a shelf life limit. Other silicon sources such as solid silicon sources have the problem of being unable to form a uniform gel. For example, in a static crystallization system, the solid silicon source will quickly sink to the bottom and stratify due to its high degree of polymerization and high density, resulting in a large deviation in the molar concentration of silicon and aluminum in the synthesis system, which leads to the formation of impure crystals uncontrollably.

[0005] Although the synthesis system of β molecular sieve without organic template is an inevitable trend, it has not yet been industrialized. The main reason is that it is impossible to achieve simple operation and stable output under industrial conditions. Therefore, how to improve the stability of the synthesis system and simplify the operation difficulty in the feeding process is of great significance to actual industrial production. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for synthesizing β molecular sieves which has simple operation steps, good repeatability, stable molecular sieve product performance and is more suitable for actual industrial production in view of the shortcomings of the above-mentioned prior art methods for synthesizing β molecular sieves without the participation of template agents.

[0007] The second object of the present invention is to provide a beta molecular sieve obtained by the synthesis method of the present invention.

[0008] The third object of the present invention is to provide the application of the beta molecular sieve obtained by the synthesis method of the present invention, especially in the liquid phase alkylation of benzene and ethylene and hydrocarbon cracking reaction.

[0009] The method for synthesizing beta molecular sieve without template provided by the present invention is characterized in that one or more silicon-containing compounds capable of reacting with an aluminum source to form a gel are used as a first silicon source, and solid silica gel is used as a second silicon source; after the first silicon source and the aluminum source react under an alkaline state to form a viscous gel, the second silicon source and a seed crystal are added to the viscous gel to form a synthetic mixture, and the synthetic mixture is hydrothermally crystallized to obtain the beta molecular sieve.

[0010] In the method provided by the present invention, the first silicon source and the aluminum source react to form a viscous gel, and the second silicon source solid silica gel and the seed crystal are evenly sealed therein. The second silicon source solid silica gel does not sink to the bottom of the crystallization reactor due to gravity, so that the solid silica gel can also react evenly with the aluminum source to form a gel under static or low stirring rate conditions.

[0011] In the method provided by the present invention, the first silicon source is a silicon-containing compound that can react with the aluminum source to form a gel, such as white carbon black, silica sol or water glass. The first silicon source can also be obtained by co-cooking silica gel with alkali metal oxides or alkali metal hydroxides.

[0012] In the method provided by the present invention, the aluminum source is a water-soluble aluminum compound, for example, one or more of sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0013] In the method provided by the present invention, the first silicon source and the aluminum source react in an alkaline state to form a viscous gel, and the viscous gel does not produce precipitation and local aggregation when left to stand for more than 2 hours at room temperature. The pH of the alkaline state is greater than 10.

[0014] In the method provided by the present invention, solid silica gel is used as the second silicon source, and the mass ratio of the first silicon source to the second silicon source is 0.5 to 2:1 in terms of SiO2.

[0015] The seed crystal is an ammonium or hydrogen beta molecular sieve, and the molar ratio of silicon oxide to aluminum oxide is 8-40, preferably 15-30; the mass ratio of the seed crystal to the silicon source in the synthesis mixture calculated as SiO2 is 1:5-20, preferably 1:7-15.

[0016] The molar ratio of the synthetic mixture is: SiO2 / Al2O3=16-50, Na / SiO2=0.40-0.65, H2O / SiO2=10-30, and the preferred molar ratio is: SiO2 / Al2O3=16-40, Na / SiO2=0.45-0.60, H2O / SiO2=15-25.

[0017] In the method provided by the present invention, the hydrothermal crystallization adopts a high and low two-stage crystallization process, that is, the crystallization is divided into two temperature sections, the first section is a high temperature section, which is conducive to the rapid growth of the molecular sieve, and the second section is a low temperature section, which is conducive to preventing the formation of impurities in the system. Preferably, the first section has a crystallization temperature of 135-150°C and a crystallization time of 15-30h, and the second section has a crystallization temperature of 110-130°C and a crystallization time of 24-48h; more preferably, the first section has a crystallization temperature of 135-145°C and a crystallization time of 20-30h, and the second section has a crystallization temperature of 115-125°C and a time of 30-40h.

[0018] In the method provided by the present invention, the hydrothermal crystallization is preferably static crystallization or dynamic crystallization at a low stirring speed, for example, the hydrothermal crystallization is carried out at a stirring rate of ≤50 rpm / min.

[0019] The present invention also provides a beta molecular sieve obtained by the above method, which can be used in the fields of petrochemical industry, preparation of fine chemicals and environmental catalysis, for example, it can be used in the alkylation reaction of benzene and ethylene and the cracking reaction of hydrocarbons.

[0020] Therefore, the present invention further provides an alkylation reaction method of benzene and ethylene, using the β molecular sieve obtained by the above method as a catalyst; and a phosphorus-modified β molecular sieve and a catalytic cracking method, wherein the phosphorus-modified β molecular sieve is obtained by modifying the β molecular sieve obtained by the above method with phosphorus, and the catalytic cracking method uses the phosphorus-modified β molecular sieve as a catalyst.

[0021] The present invention uses the alkylation reaction of benzene and ethylene and the catalytic cracking reaction of light diesel oil as probe reactions to simply verify the beta molecular sieve. The ammonium-type beta molecular sieve after ammonium exchange is calcined at 550°C for 2-6h, and the alkylation reaction of benzene and ethylene is carried out under the reaction conditions of temperature 160°C, pressure 3.0MPa, benzene-olefin ratio 7.0, mass space velocity 0.8h -1 Under the condition of 100 ℃ and 200 ℃, the ethylene conversion rate is higher than 99%, the ethylbenzene selectivity is higher than 92%, the ethylene conversion rate is about 1.5 percentage points higher than that of commercial β molecular sieve, the ethylbenzene selectivity is about 0.5 percentage points higher, and the ethylation selectivity is also slightly improved. The phosphorus-modified β molecular sieve is subjected to conventional hydrothermal aging and then subjected to light diesel cracking reaction. At the reaction temperature of 550℃, the reaction time of 70 seconds, and the mass space velocity of 1.28h -1Under the conditions, the conversion rate is greater than 70%, and the liquefied gas yield is greater than 35%. The conversion rate is at least 1 percentage point higher than that of commercial β molecular sieve, the liquefied gas yield is 1.5 percentage points higher, and the gasoline yield is basically at the same level.

[0022] The method for synthesizing beta molecular sieve without template provided by the present invention has good synthesis repeatability, high stability, simple process, low operation difficulty, and is easy to carry out industrial production. The beta molecular sieve synthesized by the method has the characteristics of pure phase, complete crystal form, and good stability, and has good application prospects in catalytic cracking, alkylation, hydrogenation, and adsorption and desorption reactions, especially compared with the currently commercially produced beta molecular sieve, it has better catalytic performance in catalytic cracking and alkylation reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD spectrum of the product of Example 1.

[0024] Figure 2 This is a SEM photograph of the product of Example 1.

[0025] Figure 3 It is the XRD spectrum of the product of Comparative Example 1.

[0026] Figure 4 It is the XRD spectrum of the product of Comparative Example 2. DETAILED DESCRIPTION

[0027] The present invention will be further described below by way of examples, but the contents of the present invention are not limited thereto.

[0028] In the examples, the X-ray diffraction (XRD) crystal phase diagram was obtained by Philips Panalytical X'pert, and the test conditions were: Cu target, Kα radiation, Ni filter, super energy detector, tube voltage 30KV, tube current 40mA.

[0029] The scanning electron microscope (SEM) images were taken by a Quanta 200F scanning electron microscope from FEI Company. The test conditions were: after drying, vacuum evaporation and gold spraying were used to increase the conductivity, and the electron microscope acceleration voltage was 20 kV.

[0030] Example 1

[0031] Add water glass (Jinan Mingchuan Chemical Co., Ltd., specific gravity 1.26, modulus 3.30) and sodium aluminate (sodium oxide 287g / L, aluminum oxide 159.7g / L) into deionized water and stir evenly until it becomes a viscous gel. While stirring, gradually add silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2) and β molecular sieve seed (Sinopec Catalyst Co., Ltd. Changling Branch, silicon-aluminum ratio 22), stirred for 1 hour until the solid was evenly dispersed. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=18, n(H2O / SiO2)=20, n(Na / SiO2)=0.60, m(seed / SiO2)=0.08, to prepare β molecular sieve precursor.

[0032] The β molecular sieve precursor was transferred to a pressure-resistant stainless steel reactor, heated to 140°C under static conditions, crystallized for 24 hours under autogenous pressure, cooled to 120°C and crystallized for 30 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample, numbered β-1.

[0033] XRD phase diagram Figure 1 , showing as β molecular sieve.

[0034] SEM images Figure 2 The grains are typical β molecular sieve stacking fault morphology.

[0035] Example 2

[0036] Add water glass (Jinan Mingchuan Chemical Co., Ltd., specific gravity 1.26, modulus 3.30) and sodium aluminate (sodium oxide 287g / L, aluminum oxide 159.7g / L) into deionized water and stir evenly until it becomes a viscous gel. While stirring, gradually add silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2 ) and β molecular sieve seed (Sinopec Catalyst Co., Ltd. Changling Branch, silicon-aluminum ratio 22), stirred for 1 hour until the solid was evenly dispersed. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=36, n(H2O / SiO2)=15, n(Na / SiO2)=0.55, m(seed / SiO2)=0.10, and a β molecular sieve precursor was prepared.

[0037] The β molecular sieve precursor was transferred to a pressure-resistant stainless steel reactor, heated to 150°C under static conditions, crystallized for 18 hours under autogenous pressure, cooled to 120°C and crystallized for 24 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample numbered β-2.

[0038] XRD phase diagram has Figure 1 The SEM image shows that the grains have Figure 2 The typical β molecular sieve stacking fault morphology characteristics are shown.

[0039] Example 3

[0040] Add water glass (Jinan Mingchuan Chemical Co., Ltd., specific gravity 1.26, modulus 3.30) and sodium aluminate (sodium oxide 287g / L, aluminum oxide 159.7g / L) into deionized water and stir evenly until it becomes a viscous gel. While stirring, gradually add silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2 ) and β molecular sieve seed (Sinopec Catalyst Co., Ltd. Changling Branch, silicon-aluminum ratio 22), stirred for 1 hour until the solid was evenly dispersed. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=20, n(H2O / SiO2)=10, n(Na / SiO2)=0.50, m(seed / SiO2)=0.15, to prepare β molecular sieve precursor.

[0041] The β molecular sieve precursor was transferred to a pressure-resistant stainless steel reactor, heated to 145°C under static conditions, crystallized for 20 hours under autogenous pressure, cooled to 120°C and crystallized for 30 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample numbered β-3.

[0042] XRD phase diagram has Figure 1 The SEM image shows that the grains have Figure 2 The typical β molecular sieve stacking fault morphology characteristics are shown.

[0043] Example 4

[0044] Silica gel (Qingdao Ocean Chemical Co., Ltd., 150-250 μm, 450 m 2 ), sodium hydroxide (Shanghai Aladdin Biochemical Technology Co., Ltd., AR, purity 96%), deionized water, stirred, heated to 120 ° C in a sealed pressure container, kept at a constant temperature for 4 hours, and cooled to obtain the first silicon source. Sodium aluminate (sodium oxide 287g / L, aluminum oxide 159.7g / L) was added to the co-cooked product, stirred until it became viscous, and silica gel powder and β molecular sieve seeds (Sinopec Catalyst Co., Ltd. Changling Branch, silicon-aluminum ratio 22) were gradually added under stirring, and stirred for 1 hour until the solid was evenly dispersed. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3) = 20, n(H2O / SiO2) = 20, n(Na / SiO2) = 0.60, m(seed / SiO2) = 0.10, and a β molecular sieve precursor was prepared.

[0045] The β molecular sieve precursor was transferred to a pressure-resistant stainless steel reactor, heated to 140°C under a static state, crystallized for 24 hours under autogenous pressure, cooled to 120°C and crystallized for 36 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample numbered β-4.

[0046] XRD phase diagram has Figure 1 The SEM image shows that the grains have Figure 2 The typical β molecular sieve stacking fault morphology characteristics are shown.

[0047] Example 5

[0048] Silica gel (Qingdao Ocean Chemical Co., Ltd., 150-250 μm, 450 m 2 ), sodium hydroxide (Shanghai Aladdin Biochemical Technology Co., Ltd., AR, purity 96%), deionized water, stirred, heated to 120 ° C in a sealed pressure container, kept at a constant temperature for 4 hours, and cooled to obtain the first silicon source. Add sodium aluminate (sodium oxide 287g / L, aluminum oxide 159.7g / L) to the co-cooked product, stir until it becomes viscous, gradually add silica gel powder and β molecular sieve seeds (Sinopec Catalyst Co., Ltd. Changling Branch, silicon-aluminum ratio 22) under stirring, and stir for 1 hour until the solid is evenly dispersed. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3) = 40, n(H2O / SiO2) = 20, n(Na / SiO2) = 0.60, m(seed / SiO2) = 0.10, and a β molecular sieve precursor is prepared.

[0049] The β molecular sieve precursor was transferred to a pressure-resistant stainless steel reactor, heated to 145°C under a static state, crystallized for 20 hours under autogenous pressure, cooled to 125°C and crystallized for 30 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample numbered β-5.

[0050] XRD phase diagram has Figure 1 The SEM image shows that the grains have Figure 2 The typical β molecular sieve stacking fault morphology characteristics are shown.

[0051] Example 6

[0052] Add water glass (Jinan Mingchuan Chemical Co., Ltd., specific gravity 1.26, modulus 3.30), sodium aluminate (sodium oxide 287g / L, aluminum oxide 159.7g / L), and sodium carbonate into deionized water and stir evenly until it becomes a viscous gel. While stirring, gradually add silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2 ) and β molecular sieve seed (Sinopec Catalyst Co., Ltd. Changling Branch, silicon-aluminum ratio 22), stirred for 1 hour until the solid was evenly dispersed. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=50, n(H2O / SiO2)=30, n(Na / SiO2)=0.65, m(seed / SiO2)=0.20, to prepare β molecular sieve precursor.

[0053] The β molecular sieve precursor was transferred to a pressure-resistant stainless steel reactor, heated to 145°C under static conditions, crystallized for 20 hours under autogenous pressure, cooled to 110°C and crystallized for 48 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample numbered β-6.

[0054] XRD phase diagram has Figure 1 The SEM image shows that the grains have Figure 2 The typical β molecular sieve stacking fault morphology characteristics are shown.

[0055] Comparative Example 1

[0056] Silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2 ), sodium aluminate, sodium hydroxide, sodium carbonate, and β molecular sieve seed were added to deionized water and stirred evenly. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=18, n(H2O / SiO2)=20, n(Na / SiO2)=0.60, m(seed

[0057] / SiO2)=0.08.

[0058] The mixture was transferred to a pressure-resistant stainless steel reactor, heated to 140°C under static conditions, crystallized for 24 hours under autogenous pressure, cooled to 120°C and crystallized for 30 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample, numbered D-1.

[0059] XRD phase diagram Figure 3 , it can be seen that it is a mixed phase of various molecular sieves.

[0060] Comparative Example 2

[0061] Water glass (Jinan Mingchuan Chemical Co., Ltd., specific gravity 1.26, modulus 3.30), sodium aluminate, sodium hydroxide, and β molecular sieve seed were added to deionized water and stirred evenly. The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=20, n(H2O / SiO2)=20, n(Na / SiO2)=0.60, m(seed / SiO2)=0.10, and a molecular sieve precursor was prepared.

[0062] The molecular sieve precursor was transferred to a pressure-resistant stainless steel reactor, heated to 140°C under static conditions, crystallized for 24 hours under autogenous pressure, cooled to 120°C and crystallized for 30 hours. After the stainless steel pressure reactor was cooled to room temperature, the solid product was separated, washed, and dried at 80°C for 12 hours to obtain a molecular sieve sample, numbered D-4.

[0063] XRD phase diagram Figure 4 , it can be seen that it is a mixed phase of various molecular sieves.

[0064] Examples 7-12

[0065] Examples 7-12 illustrate the catalytic cracking reaction effect of the beta molecular sieve of the present invention.

[0066] The β-1 sample of Example 1 was mixed with ammonium chloride and water in a mass ratio of 1:1:10, heated to 70°C and stirred for 1 hour, filtered and dried, the dried sample was ground evenly and calcined at 550°C for 2 hours, phosphoric acid was added by impregnation after calcination, wherein the amount of phosphoric acid added was 10% of the mass of the β molecular sieve, and dried at 80°C for 12 hours to obtain a phosphorus-modified hydrogen-type β molecular sieve.

[0067] The phosphorus-modified molecular sieve was crushed and 20-40 mesh particles were screened out and placed in an aging device. The temperature was raised to 800°C, 100% water vapor was introduced and kept at 800°C for 17 hours. The obtained catalyst was named β-1P. β-1P was evaluated on a fixed bed micro reactor under the following operating conditions: temperature 550°C, reaction time 70 seconds, mass space velocity 1.29h -1 , the raw material is n-tetradecane.

[0068] The evaluation results are listed in Table 1.

[0069] The samples of Examples 2-6 were treated in the same manner as in Example 7 and then evaluated in a fixed bed microreactor.

[0070] The obtained catalysts were named β-2P to β-6P.

[0071] The evaluation results are listed in Table 1.

[0072] Comparative Example 3

[0073] Comparative Example 3 is a commercial β molecular sieve (Sinopec Catalyst Co., Ltd. Changling Branch, silicon-aluminum ratio 22). The sample after phosphorus modification in the same manner as in Example 7 is named A-1 and the treatment and evaluation conditions are the same as in Example 7.

[0074] The evaluation results are listed in Table 1.

[0075] Table 1

[0076]

[0077] It can be seen from the data in Table 1 that the beta molecular sieve of the present invention has a conversion rate of at least 1 percentage point higher than that of the comparative sample in the catalytic cracking of light diesel, a liquefied gas yield of 1.5 percentage points higher, and a gasoline yield at substantially the same level.

[0078] Example 13

[0079] This example illustrates the alkylation reaction effect of the beta molecular sieve of the present invention.

[0080] The β-1 sample of Example 1 was mixed with ammonium nitrate and water in a mass ratio of 1:1:10, heated to 70°C and stirred for 1 hour, filtered and dried, and the dried sample was ground evenly and calcined at 550°C for 2 hours to obtain a hydrogen-type β molecular sieve. The hydrogen-type β molecular sieve was pressed into tablets and crushed, and 20-40 mesh particles were sieved to obtain the catalyst named β-1H.

[0081] β-1H was evaluated in a fixed bed microreactor under the following operating conditions: temperature 160°C, reaction pressure 3.0 MPa, reaction raw materials benzene and ethylene, benzene-ethylene ratio 7.0, mass space velocity 0.8 h -1 .

[0082] The evaluation results are listed in Table 2.

[0083] Comparative Example 4

[0084] Commercial β molecular sieve (Sinopec Catalyst Co., Ltd. Changling Branch, Si / Al ratio 22) was treated in the same manner as in Example 13 to obtain a catalyst named A-1H. The evaluation conditions were the same as in Example 13.

[0085] The evaluation results are listed in Table 2.

[0086] Table 2

[0087] β-1H A-1H Ethylene conversion rate (%) 99.56 98.01 Ethylbenzene selectivity (%) 93.16 92.67 Ethylation selectivity (%) 99.68 99.59

[0088] It can be seen from the data in Table 2 that when the beta molecular sieve of the present invention is used for the reaction of preparing ethylbenzene from benzene and ethylene, the ethylene conversion rate is about 1.5 percentage points higher than that of commercial beta molecular sieves, the ethylbenzene selectivity is about 0.5 percentage points higher, and the ethylation selectivity is also slightly improved.

Claims

1. A method for synthesizing beta molecular sieve without template, characterized in that: The method uses one or more silicon-containing compounds that can react with an aluminum source to form a gel as a first silicon source, and solid silica gel as a second silicon source; after the first silicon source and the aluminum source react under an alkaline state to form a viscous gel, the second silicon source and a crystal seed are added to the viscous gel to form a synthetic mixture, and the synthetic mixture is hydrothermally crystallized to obtain a β molecular sieve.

2. The method according to claim 1, characterized in that The first silicon source is selected from white carbon black, silica sol or water glass, or is obtained by co-cooking silica gel with alkali metal oxide or alkali metal hydroxide.

3. The method according to claim 1, characterized in that The aluminum source is one or more of sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum chloride.

4. The method according to claim 1, characterized in that The first silicon source and the aluminum source react in an alkaline state to form a viscous gel, and the viscous gel does not produce precipitation and local aggregation when left to stand for more than 2 hours at room temperature.

5. The method according to claim 1, characterized in that The alkaline state has a pH>10.

6. The method according to claim 1, characterized in that The mass ratio of the first silicon source to the second silicon source is 0.5 to 2:1 in terms of SiO2.

7. The method according to claim 1, characterized in that The seed crystal is an ammonium type or hydrogen type beta molecular sieve, and the molar ratio of silicon oxide to aluminum oxide is 8-40, preferably 15-30.

8. The method according to claim 1, characterized in that The molar ratio of the synthetic mixture is: SiO2 / Al2O3=16-50, Na / SiO2=0.40-0.65, H2O / SiO2=10-30, and the preferred molar ratio is: SiO2 / Al2O3=16-40, Na / SiO2=0.45-0.60, H2O / SiO2=15-25.

9. The method according to claim 1, characterized in that The mass ratio of the seed crystal to the silicon source in the synthesis mixture calculated as SiO2 is 1:5-20, preferably 1:7-15.

10. The method according to claim 1, characterized in that The hydrothermal crystallization is carried out in a closed container in two stages of high and low temperature crystallization, wherein the first stage of crystallization temperature is 135-150° C. and the crystallization time is 15-30 hours, and the second stage of crystallization temperature is 110-130° C. and the crystallization time is 24-48 hours.

11. The method according to claim 1, characterized in that The hydrothermal crystallization is carried out at a stirring rate of ≤50 rpm / min.

12. Beta molecular sieve obtained by the method of claims 1-11.

13. A method for the alkylation of benzene and ethylene, characterized in that: The beta molecular sieve of claim 12 is used as a catalyst.

14. A phosphorus-modified beta molecular sieve, characterized in that: The beta molecular sieve according to claim 12 is obtained by modifying it with phosphorus.

15. A catalytic cracking method, characterized in that: The phosphorus-modified beta molecular sieve according to claim 14 is used as a catalyst.

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