Molecular sieve and preparation method thereof

Abstract

The invention relates to the technical field of molecular sieve preparation, and particularly discloses a molecular sieve preparation method, which comprises: S1, dispersing a template agent in water, adjusting the pH value, heating to a temperature of 75-85 DEG C, adding a template silicon source and a boron-containing dopant, mixing for 2-3 h, and cooling to obtain a template slurry; s2, uniformly mixing the template slurry, a framework silicon source, an aluminum source, a nitrogen source and a structure-directing agent, adjusting the pH value, and mixing for 3.5-4.5 hours to obtain composite sol; and S3, transferring the composite sol into a reaction kettle, heating to 110-130 DEG C, carrying out hydrothermal crystallization for 34-38 hours, in an inert atmosphere, firstly heating to 300-350 DEG C, carrying out heat preservation for 1-2 hours, then heating to 450-500 DEG C, carrying out heat preservation for 2-3 hours, continuously heating to 550-600 DEG C, carrying out heat preservation for 1-2 hours, and cooling to obtain the molecular sieve. The molecular sieve prepared by the invention has relatively high CO2 permeability and selectivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve preparation, and more particularly to a molecular sieve and a preparation method thereof. BACKGROUND

[0002] In the process of natural gas exploitation and utilization, the raw gas usually contains acid gas CO2, which not only reduces the combustion heat value of natural gas, but also may form carbonic acid to corrode equipment in the pipeline. Therefore, CO2 removal is a core link in the industrial utilization of natural gas. The current mainstream CO2 separation technologies include amine absorption method, membrane separation method and molecular sieve adsorption method. Among them, the molecular sieve becomes an optimal solution for low-energy consumption decarburization due to its advantages such as simple operation and no secondary pollution.

[0003] The existing molecular sieves for natural gas decarburization are mainly 13X type and SAPO-34 type, but there are two technical bottlenecks: one is the insufficient pore adaptability. The traditional molecular sieve relies on a single physical sieving mechanism. If the pore size is reduced to improve the CO2 / CH4 selectivity, the CO2 adsorption capacity will be sharply reduced. If the pore size is increased to improve the capacity, the selectivity will be significantly reduced. In order to solve the above problems, researchers try to improve the performance of molecular sieves by element doping, pore modification and other ways.

[0004] A Chinese patent application with publication number CN120285787A discloses a method for rapidly preparing SSZ-13 molecular sieve membrane based on a double-template system. In the synthesis process of the SSZ-13 molecular sieve membrane, a double-template is used, which includes a structure-directing template and an auxiliary template. The auxiliary template is a polymer ammonium. The structure-directing template is N-N-N-trimethyladamantyl ammonium hydroxide, N-N-N-trimethyladamantyl ammonium bromide, N-N-N-trimethyladamantyl ammonium iodide or tetraethylammonium hydroxide, etc. In the specific preparation, first, the SSZ-13 molecular sieve seed is synthesized. Then, the SSZ-13 molecular sieve seed is coated on the surface of the carrier. Then, the synthesis liquid of the SSZ-13 molecular sieve membrane is prepared. Finally, the carrier obtained in step (2) and the membrane synthesis liquid obtained in step (3) are transferred to a reaction kettle, and the SSZ-13 molecular sieve membrane is obtained by hydrothermal crystallization.

[0005] In the preparation process of the above-mentioned molecular sieve membrane, two templates are needed, one is a structure-directing template, and the other is an auxiliary template. In the preparation, the SSZ-13 molecular sieve seed needs to be synthesized first, coated on the surface of the carrier, and then hydrothermally crystallized with the synthesis liquid. The coating is easy to be unevenly dispersed, and the overall steps are relatively complex, which affects the separation performance and stability of the finally prepared molecular sieve membrane. SUMMARY

[0006] In order to improve the adsorption selectivity of the existing molecular sieve in gas adsorption separation, the present application provides a molecular sieve and a preparation method thereof.

[0007] In a first aspect, the application provides a preparation method of a molecular sieve, which adopts the following technical scheme: The preparation method of the molecular sieve comprises the following steps: S1: dispersing a template agent in water, adjusting the pH to 10.5-11.5, increasing the temperature to 75-85℃, adding a template silicon source and a boron-containing dopant, mixing for 2-3h, and cooling to obtain a template slurry; S2: uniformly mixing the template slurry, a skeleton silicon source, an aluminum source, a nitrogen source, and a structure-directing agent, adjusting the pH to 10.0-11.0, mixing for 3.5-4.5h, and obtaining a composite sol; S3: transferring the composite sol to a reaction kettle, increasing the temperature to 110-130℃, and hydrothermally crystallizing for 34-38h, under an inert atmosphere, first increasing the temperature to 300-350℃, maintaining the temperature for 1-2h, then increasing the temperature to 450-500℃, maintaining the temperature for 2-3h, continuously increasing the temperature to 550-600℃, maintaining the temperature for 1-2h, and cooling to obtain the molecular sieve.

[0008] In the technical scheme, the mesoporous silica template doped with boron is constructed in advance, and the stability of the silicon-oxygen network is weakened by using boron elements, thereby significantly reducing the activation energy of the subsequent carbothermal reduction reaction. This enables the template to be efficiently and completely removed in gaseous form in the final calcination stage, thereby forming in situ a through and ordered mesoporous channel. The skeleton silicon source is self-assembled with the aluminum source and the structure-directing agent through depolymerization-recrystallization in the hydrothermal crystallization stage, thereby forming a strong skeleton with a regular microporous structure. Then, at 300-350℃, the dicyandiamide is fully decomposed to generate abundant active nitrogen-containing intermediates, which react with the silicon hydroxyl groups exposed on the surface of the molecular sieve skeleton in a gas-solid phase reaction at 450-500℃, thereby maximizing the generation of stable Si-N bonds and constructing specific adsorption sites with high selectivity for CO2. Then, at 550-600℃, the boron-doped mesoporous silica template is fully subjected to a carbothermal reduction reaction with the residual carbon, and is completely removed in gaseous form, thereby forming in situ a clear and through mesoporous channel. At the same time, the temperature further strengthens the crystal skeleton of the molecular sieve, thereby making the molecular sieve more compact and stable.

[0009] The technical scheme cooperatively constructs a hierarchical pore structure with micropores and mesopores by stepwise temperature control calcination, the micropores provide high selective adsorption of CO2 molecules through the molecular sieve effect and the surface Si-N sites, and the through mesopores serve as a high-speed diffusion channel, thereby greatly improving the mass transfer rate of CO2 molecules to the active sites inside the micropores, and thereby simultaneously achieving the unification of high adsorption selectivity and high diffusion rate.

[0010] Preferably, the boron-containing dopant is trimethyl borate or boric acid.

[0011] Preferably, the amount of the boron-containing dopant is 2% to 5% of the mass of the template silicon source.

[0012] In the technical solution, the boron-containing dopant is incorporated into the amorphous network of SiO2 in the form of BO3. 3+ The ionic radius of B is smaller than that of Si 4+ , and the coordination number is different, resulting in structural stress, bond length and bond angle distortion of the silicon-oxygen network, thereby significantly reducing the thermal stability and chemical stability of the entire template structure, making it more susceptible to attack by reducing gas and decomposition during subsequent calcination.

[0013] Preferably, in step S1, the mass ratio of the template agent to the template silicon source is 1: (4-5).

[0014] Preferably, in step S1, the template silicon source is tetraethyl orthosilicate.

[0015] Preferably, in step S1, the template agent is hexadecyl trimethyl ammonium bromide.

[0016] Preferably, in step S2, the framework silicon source is one or more of silica sol, water glass, and white carbon black.

[0017] In the technical solution, silica sol, or silica sol or / and water glass or / and white carbon black is used as the framework silicon source. The silica sol provides silicon species in the form of nanoscale colloidal silica particles, the water glass provides silicon species in the form of soluble silicate ions, and the white carbon black provides silicon species in the form of amorphous silica solid aggregates. By compounding different silicon sources, the release rate and polymerization behavior of silicon species can be controlled, thereby optimizing the crystallinity, grain size, and pore structure of the molecular sieve.

[0018] Preferably, in step S2, the aluminum source is selected from one or more of sodium metaaluminate and aluminum sulfate.

[0019] Preferably, in step S2, the aluminum source includes sodium metaaluminate and aluminum sulfate, and the molar ratio of the sodium metaaluminate to the aluminum sulfate is (2-6):1.

[0020] In the technical solution, a composite aluminum source composed of sodium metaaluminate and aluminum sulfate is used. The sodium metaaluminate provides aluminate ions with high reactivity, ensuring the nucleation efficiency. The introduction of aluminum sulfate adjusts the sodium ion concentration of the synthesis system, avoiding the generation of impurity crystals due to excessive sodium ions. The compounding of the two can synergistically promote the formation of uniform and pure molecular sieve crystal frameworks.

[0021] Preferably, in step S2, the nitrogen source is dicyandiamide.

[0022] In the technical solution, dicyandiamide is decomposed by heat in the calcination process to generate abundant nitrogen-containing active intermediates, which can react with silicon hydroxyl groups exposed on the surface of the molecular sieve framework in situ to generate Si-N active sites with extremely high thermal stability, thereby enhancing the affinity for CO2 molecules and high selectivity.

[0023] Preferably, the structure directing agent is tetrapropylammonium hydroxide.

[0024] In the technical solution, tetrapropylammonium hydroxide is used as a high-efficiency structure directing agent, and the cation thereof can precisely guide the assembly of silicoaluminate species around itself, effectively guide the formation of microporous channels, and control the size of the micropores formed.

[0025] Preferably, in step S2, the amount of the skeleton silicon source is calculated based on SiO2, the amount of the aluminum source is calculated based on Al2O3, and the molar ratio of SiO2 to Al2O3 is (25-60):1.

[0026] Preferably, the mass ratio of the amount of the skeleton silicon source calculated based on SiO2 to the amount of the template silicon source calculated based on SiO2 is (3-5):1.

[0027] Preferably, the mass ratio of the amount of the nitrogen source to the amount of SiO2 in the skeleton silicon source in step S2 is (0.4-0.6):1.

[0028] Preferably, the molar ratio of the structure directing agent to SiO2 in the skeleton silicon source in step S2 is (0.2-0.3):1.

[0029] In a second aspect, the application also provides a molecular sieve prepared by the preparation method.

[0030] The molecular sieve prepared by the technical solution has a hierarchical pore system composed of through mesopores formed by removal of the boron-doped template and intrinsic micropores of the molecular sieve, and the framework surface is rich in stable Si-N active sites, thereby effectively improving the selectivity and adsorption capacity for CO2 molecules.

[0031] Preferably, the molecular sieve can be shaped into strip-shaped, sheet-shaped or spherical adsorbent products suitable for fixed bed adsorption towers by extrusion, tabletting or rolling, etc. after being mixed with a binder.

[0032] In summary, the application has the following beneficial effects: 1. The application uses boron-doped mesoporous silica as a sacrificial template, utilizes the doping element to reduce the stability of the template silicon-oxygen network, and realizes efficient and complete removal of the template at a low temperature through a carbonthermal reduction reaction in an inert atmosphere, thereby in-situ forming a mesoporous system with uniform pore size and good throughness and maintaining the integrity of the molecular sieve crystal framework.

[0033] 2, Preferably, in the application, a composite aluminum source is used in combination with a skeleton silicon source, and a tetrapropylammonium hydroxide structure directing agent is used to effectively promote the formation of a pure and highly crystalline molecular sieve skeleton; at the same time, dicyandiamide is used as a nitrogen source to generate Si-N high-stability active sites in situ during the calcination process, thereby simultaneously achieving the construction of multi-level pores and surface functionalization treatment, and simplifying the process flow.

[0034] 3, The molecular sieve prepared by the preparation method of the application has high specific surface area, regular multi-level pores, and heat-stable adsorption sites, which enables it to exhibit synergistic advantages of high capacity, high selectivity, and excellent cycle stability in CO2 adsorption and separation, and is particularly suitable for use in the fields of natural gas purification, biogas purification, and flue gas carbon capture. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Raman spectrum of the molecular sieve in Example 1. DETAILED DESCRIPTION

[0036] The application will be further described in detail below in combination with examples.

[0037] The raw materials of the examples and comparative examples of the application are all ordinary commercially available, except for special instructions.

[0038] Example 1 The preparation method of the molecular sieve of the present embodiment comprises the following steps: S1: 5.2 g of cetyltrimethylammonium bromide and 500 mL of deionized water were added to a reactor, stirred and mixed uniformly at a rotation speed of 300 rpm, the pH was adjusted to 11.0 using 5% sodium hydroxide by mass fraction, the temperature was raised to 80℃, and 23.4 g of tetraethyl orthosilicate and 0.82 g of trimethyl borate were slowly added, and after stirring and mixing for 2.5 h, a template slurry was prepared; S2: In the template slurry, 90.0 g of silica sol, 1.64 g of sodium alumininate, 13.5 g of dicyandiamide, and 22.4 g of tetrapropylammonium hydroxide were slowly added and stirred and mixed uniformly, then the pH was adjusted to 10.5 using 5% sodium hydroxide by mass fraction, and stirring and mixing was continued for 4 h to obtain a composite sol; S3: The composite gel was transferred to a high-pressure reaction kettle, first heated to 120℃ at a rate of 1℃ / min, hydrothermally crystallized for 36 h, high-purity nitrogen was introduced, then heated to 300℃ at a rate of 2℃ / min, kept for 2 h, then heated to 500℃ at a rate of 1℃ / min, kept for 2 h, then heated to 550℃ at a rate of 2℃ / min, kept for 2 h, and then naturally cooled to room temperature under nitrogen protection to obtain the molecular sieve.

[0039] The mass concentration of the silica sol is 30%, 90.0 g of the silica sol is about 0.45 mol of SiO2, the amount of sodium aluminate is about 0.02 mol, and the molar mass of tetraethyl orthosilicate is calculated according to 208.3 g / mol; the molar mass of SiO2 is calculated according to 60 g / mol; and the molar mass of sodium aluminate is calculated according to 82 g / mol.

[0040] Example 2 The preparation method of the molecular sieve in the example includes the following steps: S1: 4.4 g of cetyltrimethylammonium bromide and 500 mL of deionized water were added to a reactor, stirred and uniformly mixed at a rotation speed of 300 rpm, the pH was adjusted to 10.5 by using 5% sodium hydroxide, the temperature was raised to 85℃, and 17.4 g of tetraethyl orthosilicate and 0.35 g of boric acid were slowly added dropwise, and after stirring and mixing for 2 h, a template slurry was prepared; S2: In the template slurry, 50.0 g of silica sol, 1.64 g of sodium aluminate, 6 g of dicyandiamide and 10.2 g of tetrapropylammonium hydroxide were slowly added and uniformly stirred and mixed, and then the pH was adjusted to 10 by using 5% sodium hydroxide, and stirring and mixing was continued for 3.5 h to obtain a composite sol; S3: The composite gel was transferred to a high-pressure reaction kettle, first heated to 110℃ at a rate of 1℃ / min, hydrothermally crystallized for 38 h, high-purity nitrogen was introduced, then heated to 350℃ at a rate of 2℃ / min, kept for 1 h, then heated to 450℃ at a rate of 1℃ / min, kept for 3 h, then heated to 600℃ at a rate of 2℃ / min, kept for 1 h, and then naturally cooled to room temperature under the protection of nitrogen to obtain the molecular sieve.

[0041] The mass concentration of the silica sol is 30%, 90.0 g of the silica sol is about 0.45 mol of SiO2, the amount of sodium aluminate is about 0.02 mol, and the molar mass of tetraethyl orthosilicate is calculated according to 208.3 g / mol; the molar mass of SiO2 is calculated according to 60 g / mol; and the molar mass of sodium aluminate is calculated according to 82 g / mol.

[0042] Example 3 The preparation method of the molecular sieve in the example includes the following steps: S1: 5 g of cetyltrimethylammonium bromide and 500 mL of deionized water were added to a reactor, stirred and uniformly mixed at a rotation speed of 300 rpm, the pH was adjusted to 11.5 by using 5% sodium hydroxide, the temperature was raised to 75℃, and 25.0 g of tetraethyl orthosilicate and 1.25 g of trimethyl borate were slowly added dropwise, and after stirring and mixing for 3 h, a template slurry was prepared; S2: slowly add silica sol 120.0 g, sodium alumininate 1.64 g, dicyandiamide 21.6 g and tetrapropylammonium hydroxide 36.6 g into the template slurry, mix uniformly, then adjust pH to 11 by using 5% sodium hydroxide, continue to mix for 4.5 h, to obtain a composite sol; S3: transfer the composite gel into a high-pressure reactor, first heat to 130℃ at 1℃ / min, hydrothermally crystallize for 34 h, then pass high-purity nitrogen, heat to 350℃ at 2℃ / min, keep for 1.5 h, then heat to 500℃ at 1℃ / min, keep for 3 h, then heat to 600℃ at 2℃ / min, keep for 1.5 h, naturally cool to room temperature under nitrogen protection, to obtain the molecular sieve.

[0043] The mass concentration of the silica sol is 30%, 120 g of silica sol is about 0.6 mol of SiO2, the amount of sodium alumininate is about 0.02 mol, the molar mass of tetraethyl orthosilicate is calculated according to 208.3 g / mol; the molar mass of SiO2 is calculated according to 60 g / mol; and the molar mass of sodium alumininate is calculated according to 82 g / mol.

[0044] Example 4 The difference between this example and Example 3 is that: S2: slowly add silica sol 120.0 g, sodium alumininate 1.23 g, aluminum sulfate 0.86 g, dicyandiamide 21.6 g and tetrapropylammonium hydroxide 36.6 g into the template slurry, mix uniformly, then adjust pH to 11 by using 5% sodium hydroxide, continue to mix for 4.5 h, to obtain a composite sol; The molar mass of aluminum sulfate is calculated according to 342.2 g / mol, the amount of sodium alumininate is 0.015 mol, and the amount of aluminum sulfate is 0.0025 mol.

[0045] The others are the same as in Example 3.

[0046] Example 5 The difference between this example and Example 4 is that: S2: slowly add silica sol 72 g, white carbon black 14.4 g, sodium alumininate 1.23 g, aluminum sulfate 0.86 g, dicyandiamide 21.6 g and tetrapropylammonium hydroxide 36.6 g into the template slurry, mix uniformly, then adjust pH to 11 by using 5% sodium hydroxide, continue to mix for 4.5 h, to obtain a composite sol; The purity of the white carbon black is 99%.

[0047] The others are the same as in Example 4.

[0048] Example 6 The difference between the present example and Example 5 is that: S2: In the template slurry, slowly add silica sol 60 g, white carbon black 10.8 g, water glass 20.6 g, sodium metaaluminate 0.82 g, aluminum sulfate 1.7 g, dicyandiamide 21.6 g and tetrapropylammonium hydroxide 36.6 g, stir and mix uniformly, then adjust the pH to 11 with 5% sodium hydroxide by mass fraction, continue to stir and mix for 4.5 h, to obtain a composite sol; Among them, the content of silicon dioxide in water glass is 35%, the amount of sodium metaaluminate is 0.01 mol, and the amount of aluminum sulfate is 0.005 mol.

[0049] The others are the same as Example 5.

[0050] Comparative Example 1 The difference between the present example and Example 1 is that: S1: Put cetyltrimethylammonium bromide 5.2 g and deionized water 500 mL into the reactor, stir and mix uniformly at a speed of 300 rpm, adjust the pH to 11.0 with 5% sodium hydroxide by mass fraction, heat to 80℃, slowly add tetraethyl orthosilicate 23.4 g, stir and mix for 2.5 h, to obtain a template slurry; The others are the same as Example 1.

[0051] Comparative Example 2 The difference between the present example and Example 1 is that: S2: In the template slurry, slowly add silica sol 90.0 g, sodium metaaluminate 1.64 g and tetrapropylammonium hydroxide 22.4 g, stir and mix uniformly, then adjust the pH to 10.5 with 5% sodium hydroxide by mass fraction, continue to stir and mix for 4 h, to obtain a composite sol; The others are the same as Example 1.

[0052] Performance test The molecular sieves prepared in Examples 1-6 and Comparative Examples 1-2 were tested for CO2 / CH4 gas separation, at a temperature of 25℃, a pressure of 0.2 MPa, a feed gas flow rate of 100 mL / min, a molar ratio of CO2:CH4 of 1:1, and nitrogen gas as a purge gas into the cavity at a flow rate of 50 mL / min. In addition, the pore volume, residual boron content and surface nitrogen content of the molecular sieves were also tested, and the test results are shown in Table 1.

[0053] Table 1 Performance test of molecular sieves prepared in Examples 1-6 and Comparative Examples 1-2

[0054] In Examples 1-6, the boron-doped templates were successfully removed, forming a developed through mesoporous system. These mesopores serve as rapid transport channels for gas molecules, thus exhibiting high CO2 permeability. Meanwhile, the dicyandiamide was in-situ pyrolyzed during calcination, and its nitrogen-containing active intermediates reacted with the silicon hydroxyl groups on the surface of the molecular sieve framework to generate a large number of stable Si-N specific adsorption sites. These sites have a strong affinity for CO2 molecules and a weak interaction with CH4 molecules, thus endowing the molecular sieve with high CO2 / CH4 separation selectivity.

[0055] In Comparative Example 1, without boron doping, the mesoporous silica template is stable in structure and difficult to be effectively removed by the carbothermal reduction reaction under calcination conditions, partially blocking the pores of the molecular sieve, hindering the rapid mass transfer of gas, and also wrapping the species produced by the decomposition of the nitrogen source, so that the Si-N sites cannot be effectively formed on the surface of the molecular sieve.

[0056] In Comparative Example 2, although the boron-doped template removal forms developed mesoporous channels, making its CO2 permeability comparable to that of the examples, the surface of the molecular sieve framework lacks Si-N specific adsorption sites generated by the decomposition of the nitrogen source. Its separation of CO2 and CH4 mainly relies on the size screening and van der Waals force of the micropores of the molecular sieve, thus the separation selectivity is much lower than that of the examples, proving that in-situ nitrogenation functionalization is an indispensable key role for achieving ultra-high selectivity.

[0057] In combination Figure 1 Analysis shows that the molecular sieve prepared in Example 1 exhibits Raman peaks at 286 cm -1 , 361 cm -1 , 380 cm -1 , 801 cm -1 , 936 cm -1 , and 1047 cm -1 . No boron characteristic peak is observed in the spectrum, confirming that the boron doping is successfully removed, triggering the carbothermal reduction reaction of the mesoporous silica template, thus forming a developed through mesoporous system, providing a rapid transport channel for gas molecules, and laying the foundation for high CO2 permeability. In addition, the clear Si-N bond vibration peak at 936 cm -1 indicates that the nitrogen-containing active intermediates generated by the in-situ pyrolysis of dicyandiamide react with the silicon hydroxyl groups on the surface of the framework to generate specific adsorption sites, which have a very high affinity for CO2 molecules. Meanwhile, the structural characteristic peaks at 286 cm -1 and 380 cm -1 , the Brønsted acid site peak at 361 cm -1 , and the peaks at 801 cm -1 and 1047 cm -1The presence of the siloxane skeleton peak indicates that the microporous crystal structure of the molecular sieve is kept intact during the pore-forming and nitridation functionalization processes, ensuring the stability of the material.

[0058] The specific embodiments are only illustrative of the application and are not intended to limit the application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the application, they are protected by the patent law.

Claims

1. A method for preparing a molecular sieve, characterized in that: The steps include: S1: Disperse the template agent in water, adjust the pH to 10.5-11.5, heat to 75-85°C, add the template silicon source and boron-containing dopant, mix for 2-3 hours, and cool to obtain the template slurry; S2: The template slurry, skeleton silicon source, aluminum source, nitrogen source and structure directing agent are mixed evenly, the pH is adjusted to 10.0-11.0, and the mixture is mixed for 3.5-4.5 hours to obtain a composite sol; S3: Transfer the composite sol to a reactor, heat it to 110-130°C, and hydrothermally crystallize it for 34-38 hours. Under an inert atmosphere, first heat it to 300-350°C, keep it warm for 1-2 hours, then heat it to 450-500°C, keep it warm for 2-3 hours, continue to heat it to 550-600°C, keep it warm for 1-2 hours, and cool it to obtain a molecular sieve.

2. The method for preparing molecular sieve according to claim 1, characterized in that: The boron-containing dopant is trimethyl borate or boric acid.

3. The method for preparing molecular sieve according to claim 2, characterized in that: The amount of the boron-containing dopant is 2% to 5% of the mass of the template silicon source.

4. The method for preparing molecular sieve according to claim 1, characterized in that: In step S2, the skeleton silicon source is one or more of silica sol, water glass, and white carbon black.

5. The method for preparing molecular sieve according to claim 1, characterized in that: In step S2, the aluminum source is selected from one or more of sodium metaaluminate and aluminum sulfate.

6. The method for preparing molecular sieve according to claim 1, characterized in that: In step S2, the aluminum source includes sodium aluminate and aluminum sulfate, and the molar ratio of the sodium aluminate to the aluminum sulfate is (2-6):

1.

7. The method for preparing molecular sieve according to claim 1, characterized in that: In step S2, the nitrogen source is dicyandiamide.

8. The method for preparing molecular sieve according to claim 1, characterized in that: In step S2, the amount of the skeleton silicon source is calculated as SiO2, the amount of the aluminum source is calculated as Al2O3, and the molar ratio of SiO2 to Al2O3 is (25~60):

1.

9. The method for preparing molecular sieve according to claim 1, characterized in that: The mass ratio of the skeleton silicon source, calculated as SiO2, to the template silicon source, calculated as SiO2, is (3-5):

1.

10. A molecular sieve prepared by the method for preparing a molecular sieve according to claim 1.

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