A method for preparing multi-level pore pure silicon Silicalite-1 molecular sieve

Abstract

The present invention provides a method for preparing a multi-level pore pure silicon Silicalite-1 molecular sieve. The method comprises: mixing a silicon source with water, a first template, and a seed, stirring for 0.5-5h at 20-80°C for pretreatment to obtain a pretreated silicon source mixed solution; wherein the first template comprises at least one of methanol, ethanol, and ethylene glycol; mixing the pretreated silicon source mixed solution with an alkali source, a seed, and a first template, stirring for 1-5h at 20-80°C, and then adding a second template and continuing to stir for 1-10h to obtain a crystallized gel; wherein the second template comprises at least one of ethanol, ethylene glycol, and n-butanol, and the second template is different from the first template; the crystallized gel is crystallized at 150-180°C for 10-72h to obtain a multi-level pore pure silicon Silicalite-1 molecular sieve.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and in particular relates to a method for preparing a multi-level pore pure silicon Silicalite-1 molecular sieve. Background Art

[0002] ZSM-5 molecular sieve (MFI) has excellent selective catalytic performance, and its unique three-dimensional cross-pore system provides abundant pores for mass transfer of reactants and products in the catalytic process. The framework structure of pure silicon Silicalite-1 molecular sieve is the same as that of ZSM-5 and belongs to the MFI type. It has strong hydrophobic properties and good olefin desorption properties, and is widely used in the preparation of adsorbents and carbon dioxide hydrogenation catalysts. Pure silicon Silicalite-1 molecular sieve is widely used in the synthesis of active metal doping and molecular sieve membranes due to its high structural stability, such as coating nickel particles with a layer of Silicalite-1 molecular sieve membrane for methane dry reforming reaction, such as synthesizing graded nano multifunctional catalysts by doping zinc zirconium in Silicalite-1 molecular sieve for direct conversion of ethanol to butadiene.

[0003] CN105668579A discloses the synthesis of mesoporous Silicalite-1 molecular sieve using seed crystals and organic amine templates, wherein seed crystals, silica sol, ethylamine, tetrapropylammonium bromide, sodium oxide, ethyl orthosilicate, ethanol and deionized water are mixed and stirred for 24 hours, then crystallized at 100°C for 72 hours, and the product is obtained by repeated centrifugation, and the product has a relatively rich pore structure. However, the method uses a large amount of seed crystals (10%) and requires the use of organic amines, which is costly to synthesize, takes a long time to crystallize, and has cumbersome steps for separating the products.

[0004] CN105645425A discloses the synthesis of mesoporous Silicalite-1 molecular sieves using white carbon black as a silicon source, seed crystals and organic amine templates, and the particle size of the synthesized product is relatively small (<1 μm). However, the process of dissolving white carbon black in water is very likely to cause dust pollution and the density of the mixed liquid is different. The crystallization process requires extremely high stirring effect, the product crystallinity is difficult to guarantee, the amount of seed crystals used is large (10%), and the cost of using organic amine synthesis is high.

[0005] CN103466653A discloses a method for preparing a pure silicon Silicalite-1 molecular sieve, which uses tetrapropylammonium hydroxide as a template, mixes the template with a silicon source, adds a silane coupling agent to the system, drips sulfuric acid to adjust the pH, mixes evenly, and then moves into a crystallization kettle for crystallization to obtain a molecular sieve product, which has a relatively rich pore structure. However, the process uses a large amount of organic amine templates, which has a high synthesis cost, and the use of sulfuric acid is highly corrosive and is not conducive to safe production.

[0006] After more than 40 years of continuous development, Silicalite-1 molecular sieve has formed synthetic routes such as organic amine template method and seed crystal method. However, the existing system still uses a large amount of organic amine template after replacing tetraethyl orthosilicate with silicon sources such as silica sol. This method has high production cost and heavy pollution. When using the seed crystal method, excessive seed input also leads to increased production costs.

[0007] For this reason, there is an existing technology that proposes to use low-carbon alcohols as templates to synthesize pure silicon Silicalite-1 molecular sieves. In the prior art, when using low-carbon alcohols as templates to synthesize pure silicon Silicalite-1 molecular sieves, it is necessary to use a grinding method in combination with a steam-assisted method to stably obtain pure silicon Silicalite-1 molecular sieves with high crystallinity. In the synthesis process of its non-aqueous system, low-carbon alcohols play a role in pore filling, and the low-carbon alcohols in the product can be removed and reused by washing. However, the grinding method and the steam-assisted method have low single-pot feed amounts. When the raw material input amount increases, due to the limitation of material mixing in the grinding method, the excess silicon source is prone to agglomeration to form γ-SiO2 or magadiite in an environment where it cannot be induced into an MFI structure crystal nucleus. Therefore, the existing technology for synthesizing pure silicon Silicalite-1 molecular sieves using low-carbon alcohols as templates cannot be promoted industrially.

[0008] As mentioned above, there is still a need to study a method for synthesizing pure silicon Silicalite-1 molecular sieve using cheap silica sol as a silicon source and low-carbon alcohol non-organic amines as templates, so as to improve the practical significance of using alcohols as templates to prepare pure silicon MFI structure molecular sieves. Summary of the invention

[0009] The purpose of the present invention is to provide a technical solution for preparing multi-level pore pure silicon Silicalite-1 molecular sieve using cheap and environmentally friendly low-carbon alcohol as a template agent, which is helpful for achieving industrial promotion. The technical solution can realize the preparation of multi-level pore pure silicon Silicalite-1 molecular sieve in simple steps using a variety of silicon sources including cheap silica sol.

[0010] In order to achieve the above object, the present invention provides a method for preparing a multi-level pore pure silicon Silicalite-1 molecular sieve, wherein the method comprises:

[0011] The silicon source is mixed with water, a first template agent, and a seed crystal, and stirred at 20-80° C. for 0.5-5 hours for pretreatment to obtain a pretreated silicon source mixed solution; wherein the first template agent includes at least one of methanol, ethanol, and ethylene glycol;

[0012] The pretreated silicon source mixed solution is mixed with an alkali source, a seed crystal, and a first template, and after stirring at 20-80° C. for 1-5 hours, a second template is added and stirred for 1-10 hours to obtain a crystallized gel; wherein the second template comprises at least one of ethanol, ethylene glycol, and n-butanol; and wherein the second template is of a different type from the first template;

[0013] The crystallized gel is crystallized at 150-180° C. for 10-72 hours to obtain a multi-level pore pure silicon Silicalite-1 molecular sieve.

[0014] According to a preferred embodiment of the above preparation method, the seed crystal is prepared by the following method:

[0015] Tetrapropylammonium hydroxide, ethyl orthosilicate and water in a molar ratio of 1TPAOH:(4.5-5.5)TEOS:(150-180)H2O are mixed and stirred for 8.0-12.0h, then crystallized at 55-65°C for 45-50h, and cooled to obtain a crystallized stock paste; the crystallized stock paste is mixed with water in a mass ratio of 1 crystallized stock paste:(8-12)H2O to obtain a seed crystal.

[0016] According to a preferred embodiment of the above-mentioned preparation method, during the preparation of the pretreated silicon source mixed solution, the silicon source is mixed with water, the first template and the seed crystals according to the mass feed ratio of 1SiO2: (0.1-0.5)H2O: (0.1-0.2) first template: (0.04-0.08) seed crystals.

[0017] According to a preferred embodiment of the above preparation method, mixing the silicon source with water, the first template, and the seed crystal comprises:

[0018] Mix the silicon source with water, heat to 35-45°C, add seed crystals and stir for 0.5-1.5h, then add the first template dropwise.

[0019] According to a preferred embodiment of the above preparation method, the temperature for pretreatment is 30-60°C.

[0020] According to a preferred embodiment of the above preparation method, the first template includes at least one of methanol and ethanol.

[0021] According to a preferred embodiment of the above preparation method, the silicon source includes at least one of alkaline silica sol, neutral silica sol, acidic silica sol, white carbon black, solid silica gel and ethyl orthosilicate;

[0022] Further, the silicon source includes at least one of alkaline silica solution and white carbon black.

[0023] According to a preferred embodiment of the above preparation method, during the preparation of the crystallized gel, the mass ratio of the pretreated silicon source mixture, the alkali source, the seed crystal, the first template, and the second template is: 1: (0.02-0.04): (0.05-0.15): (0.2-0.4): (0.05-0.15).

[0024] According to a preferred embodiment of the above preparation method, the pretreated silicon source mixed solution is mixed with an alkali source, a seed crystal, and a first template agent, comprising:

[0025] Add an alkali source to the pretreated silicon source mixture, stir for no more than 1.0 hour, then heat to 45-55° C., add a seed crystal, stir for 0.5-1.5 hours, then add the first template.

[0026] According to a preferred embodiment of the above preparation method, during the preparation of the crystallized gel, the pretreated silicon source mixture is mixed with the alkali source, the seed crystal, and the first template, stirred at 30-70°C for 1-5h, and then the second template is added and stirred for 1-10h to obtain the crystallized gel.

[0027] According to a preferred embodiment of the above preparation method, the second template is n-butanol.

[0028] According to a preferred embodiment of the above preparation method, the alkali source includes at least one of sodium hydroxide and potassium hydroxide.

[0029] According to a preferred embodiment of the above preparation method, the crystallization temperature is 160-175° C., and the crystallization time is 15-40 h.

[0030] According to a preferred embodiment of the above preparation method, the method further comprises: washing, filtering, drying and calcining the crystallized product;

[0031] Furthermore, the calcination temperature is 500-600° C., and the calcination time is 4.0-6.0 h.

[0032] The preparation method of the multi-level pore pure silicon Silicalite-1 molecular sieve provided by the present invention adopts a "one-step method" to hydrothermally synthesize the pure silicon Silicalite-1 molecular sieve. The silicon source is pretreated, and the material mixing order of the pretreated silicon source and the template agent is strictly limited to obtain a uniform high-activity crystallization mother solution, and finally a low-carbon alcohol is used as a template agent and a very small amount of seed crystals (<2.0%, mSiO2 in the seed crystals / mSiO2 in the feed) is added to synthesize the pure silicon Silicalite-1 molecular sieve product through the synergistic effect of alcohol-seed crystals. By strictly limiting the mixing time and adding order of the first template agent and the second template agent and adjusting the dosage ratio, finally a high-crystallinity multi-level pore pure silicon Silicalite-1 molecular sieve product is synthesized using low-carbon alcohol as a dual template agent, so that the synthesis cost and environmental pollution cost are significantly reduced, which has great practical application significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The XRD spectrum of the molecular sieve product synthesized in Example 1 of the present invention.

[0034] Figure 2 This is a SEM spectrum of the molecular sieve product synthesized in Example 1 of the present invention.

[0035] Figure 3 This is the XRD spectrum of the molecular sieve product synthesized in Example 3 of the present invention.

[0036] Figure 4 This is a SEM spectrum of the molecular sieve product synthesized in Example 3 of the present invention.

[0037] Figure 5 This is the XRD spectrum of the molecular sieve product synthesized in Example 4 of the present invention.

[0038] Figure 6 This is a SEM spectrum of the molecular sieve product synthesized in Example 4 of the present invention.

[0039] Figure 7 This is the XRD spectrum of the molecular sieve product synthesized in Example 5 of the present invention.

[0040] Figure 8 This is the SEM spectrum of the molecular sieve product synthesized in Example 5 of the present invention.

[0041] Fig. 9 This is the XRD spectrum of the molecular sieve product synthesized in Comparative Example 2 of the present invention.

[0042] Fig.10 This is the XRD spectrum of the molecular sieve product synthesized in Comparative Example 3 of the present invention.

[0043] Fig.11 This is the nitrogen adsorption spectrum of the molecular sieve product synthesized in Example 1 of the present invention.

[0044] Fig.12 This is a pore size distribution diagram of the molecular sieve product synthesized in Example 1 of the present invention. DETAILED DESCRIPTION

[0045] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0046] Raw materials used in the examples:

[0047] First template: methanol (98%), ethanol (97%), ethylene glycol (98%);

[0048] Second template: ethanol (97%), ethylene glycol (98%), n-butanol (99%);

[0049] Silicon source: alkaline silica sol (SiO2 content 30wt%, Na2O <0.4wt%), neutral silica sol (SiO2 content 30wt%, Na2O <0.2wt%), acidic silica sol (SiO2 content 30wt%, Na2O <0.006wt%), white carbon black (fumed silica SiO2 content 92wt%), solid silica gel (SiO2 content 95wt%), ethyl orthosilicate (98wt%);

[0050] Alkali source: sodium hydroxide (99wt%), potassium hydroxide (99wt%);

[0051] Seed: Tetrapropylammonium hydroxide, ethyl orthosilicate and deionized water in a molar ratio of 5.1:25:800 were mixed and stirred for 10.0 h, then put into a crystallization kettle and crystallized at 60°C for 48.0 h, then naturally cooled to room temperature to obtain a crystallization slurry, and the crystallization slurry was diluted with deionized water in a mass ratio of 1:10 to obtain a liquid seed aqueous solution as a seed for standby use.

[0052] Example 1

[0053] This embodiment provides a method for preparing a multi-level porous pure silicon Silicalite-1 molecular sieve, wherein the method comprises:

[0054] Add 25.0 g of deionized water to 100.0 g of alkaline silica sol, heat to 40° C., add 2.0 g of seed crystals, stir for 1.0 h, add 10.0 g of methanol dropwise, stir vigorously for 1.0 h, and obtain a pretreated silicon source mixed solution;

[0055] 1.5 g of sodium hydroxide particles were added to the pretreated silicon source mixture, stirred for 0.5 h, then heated to 50°C, 1.0 g of seed crystals were added, and 10.0 g of methanol was added after vigorous stirring for 1.0 h. After stirring for 2.0 h until the solution was clarified, 2.0 g of n-butanol was added dropwise, and vigorous stirring was performed for 2.0 h to obtain a crystallized gel, which was then crystallized at 170°C for 42.0 h. The crystallized product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain a pure silicon Silicalite-1 molecular sieve product.

[0056] The XRD spectrum of the multi-level pore pure silicon Silicalite-1 molecular sieve product prepared in this example is shown in Figure 1 .Depend on Figure 1 It can be seen that the multi-level pore pure silicon Silicalite-1 molecular sieve product prepared in this example has a typical MFI structural characteristic peak. Figure 2 This is a SEM picture of the multi-level porous pure silicon Silicalite-1 molecular sieve product prepared in this example. The product has a hexagonal prism morphology. Fig.11 This is the nitrogen adsorption spectrum of the multi-level pore pure silicon Silicalite-1 molecular sieve product prepared in this example. Fig.12 This is the pore size distribution diagram of the molecular sieve product synthesized in Example 1 of the present invention. The specific surface area of ​​the product was measured by BET (N2 adsorption). The total specific surface area was 241.5 and the number of mesopores was 88.1.

[0057] Example 2

[0058] This embodiment provides a method for preparing a multi-level porous pure silicon Silicalite-1 molecular sieve, wherein the method comprises:

[0059] Add 25.0 g of deionized water to 100.0 g of alkaline silica sol, heat to 40° C., add 3.0 g of seed crystals, stir for 1.0 h, add 20.0 g of ethanol dropwise, stir vigorously for 0.5 h, and obtain a pretreated silicon source mixed solution;

[0060] 1.2 g of sodium hydroxide particles were added to the pretreated silicon source mixed solution, and the mixture was heated to 60°C after stirring for 1.0 h, and 3.0 g of seed crystals were added. After vigorous stirring for 0.5 h, 28.0 g of ethanol was added. After stirring for 2.0 h until the solution was clarified, 1.5 g of n-butanol was added dropwise. After vigorous stirring for 1.0 h, a crystallized gel was obtained, which was then crystallized at 170°C for 45.0 h. The crystallized product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain a pure silicon Silicalite-1 molecular sieve product.

[0061] The multi-level porous pure silicon Silicalite-1 molecular sieve product prepared in this example has a typical MFI structural characteristic peak. The specific surface area of ​​the product is measured by BET (N2 adsorption), and its total specific surface area is 323.2, and the number of mesopores is 98.8.

[0062] Example 3

[0063] This embodiment provides a method for preparing a multi-level porous pure silicon Silicalite-1 molecular sieve, wherein the method comprises:

[0064] Add 95.0 g of deionized water to 30.0 g of white carbon black, heat to 40°C, add 5.0 g of seed crystals, stir for 3.0 h, then add 30.0 g of methanol dropwise, stir vigorously for 2.0 h to obtain a pretreated silicon source mixed solution;

[0065] 1.1 g of sodium hydroxide particles were added to the pretreated silicon source mixture, and the mixture was heated to 60°C after being vigorously stirred for 0.5 h. 2.0 g of seed crystals were added. After being vigorously stirred for 1.0 h, 15.0 g of methanol was added. After being stirred for 2.0 h, 2.0 g of n-butanol was added dropwise. After being vigorously stirred for 1.0 h, a crystallized gel was obtained, which was then crystallized at 175°C for 36.0 h. The crystallized product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain a pure silicon Silicalite-1 molecular sieve product.

[0066] The XRD pattern of the multi-level pore pure silicon Silicalite-1 molecular sieve product prepared in this example is shown in Figure 3 , the product has typical MFI structural characteristic peaks. Figure 4 This is the SEM picture of the multi-level porous pure silicon Silicalite-1 molecular sieve product prepared in this example. The specific surface area of ​​the product was measured by BET (N2 adsorption). The total specific surface area was 269.8 and the number of mesopores was 55.8.

[0067] Example 4

[0068] This embodiment provides a method for preparing a multi-level porous pure silicon Silicalite-1 molecular sieve, wherein the method comprises:

[0069] Add 30.0 g of deionized water to 100.0 g of alkaline silica sol, heat to 40° C., add 4.0 g of seed crystals, stir for 1.5 h, add 30.0 g of methanol dropwise, stir vigorously for 1.0 h, and obtain a pretreated silicon source mixed solution;

[0070] 1.6 g of sodium hydroxide particles were added to the pretreated silicon source mixed solution, and the mixture was stirred for 0.5 h and then heated to 50°C. 6.0 g of seed crystals were added, and 10.0 g of methanol was added after vigorous stirring for 1.0 h. After stirring for 1.0 h until the solution was clarified, 2.0 g of n-butanol was added dropwise and stirred vigorously for 2.0 h to obtain a crystallized gel. The mixture was then crystallized at 100°C for 20.0 h and then heated to 170°C for crystallization for 30.0 h. The crystallized product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain a pure silicon Silicalite-1 molecular sieve product.

[0071] The XRD pattern of the multi-level pore pure silicon Silicalite-1 molecular sieve product prepared in this example is shown in Figure 5 , the product has typical MFI structural characteristic peaks. Figure 6 This is the SEM picture of the multi-level porous pure silicon Silicalite-1 molecular sieve product prepared in this example. The specific surface area of ​​the product was measured by BET (N2 adsorption). The total specific surface area was 354.5 and the number of mesopores was 157.5.

[0072] Example 5

[0073] This embodiment provides a method for preparing a multi-level porous pure silicon Silicalite-1 molecular sieve, wherein the method comprises:

[0074] Add 40.0 g of deionized water to 200.0 g of ethyl orthosilicate, heat to 50° C., add 4.0 g of seed crystals, stir for 1 h, then slowly add 35.0 g of ethanol dropwise, stir vigorously for 2.0 h, and obtain a pretreated clarified silicon source mixed solution.

[0075] 2.8 g of potassium hydroxide particles were added to the pretreated clarified silicon source mixed solution, the temperature was raised to 60°C after stirring for 0.5 h, 2.0 g of seed crystals were added, 25.0 g of ethanol was added after vigorous stirring for 0.5 h, 4.0 g of ethylene glycol was added dropwise after stirring for 2.0 h until the solution was clarified, and a crystallized gel was obtained after stirring for 2.5 h, which was then crystallized at 180°C for 72.0 h. The product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain a pure silicon Silicalite-1 molecular sieve product.

[0076] The XRD pattern of the multi-level pore pure silicon Silicalite-1 molecular sieve product prepared in this example is shown in Figure 7 , the product has typical MFI structural characteristic peaks. Figure 8 This is the SEM picture of the multi-level porous pure silicon Silicalite-1 molecular sieve product prepared in this example. The specific surface area of ​​the product was measured by BET (N2 adsorption). The total specific surface area was 348.5 and the number of mesopores was 42.6.

[0077] Example 6

[0078] This embodiment provides a method for preparing a multi-level porous pure silicon Silicalite-1 molecular sieve, wherein the method comprises:

[0079] 30.0 g of deionized water was added to 100.0 g of alkaline silica sol, the temperature was raised to 50° C., 3.0 g of seed crystals were added, and after stirring for 0.5 h, 17.0 g of ethylene glycol was added dropwise, and the mixture was vigorously stirred for 1.0 h to obtain a pretreated silicon source mixed solution.

[0080] 1.3 g of sodium hydroxide particles were added to the pretreated silicon source mixed solution, and the temperature was raised to 60°C after stirring for 0.5 h. 3.0 g of seed crystals were added, and the solution was clarified after vigorous stirring for 1.0 h. 17.0 g of ethylene glycol was added, and the solution was clarified after stirring for 2.0 h. 2.0 g of n-butanol was added dropwise, and the solution was vigorously stirred for 1.0 h to obtain a crystallized gel, which was then crystallized at 170°C for 36.0 h. The crystallized product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain a pure silicon Silicalite-1 molecular sieve product.

[0081] The multi-level pore pure silicon Silicalite-1 molecular sieve product prepared in this example has a typical MFI structural characteristic peak. The specific surface area of ​​the product is measured by BET (N2 adsorption), and its total specific surface area is 288.2, and the number of mesopores is 65.8.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing a molecular sieve, wherein the method comprises:

[0084] 1.5 g of sodium hydroxide particles were dissolved in 25.0 g of deionized water, 20.0 g of methanol and 3.0 g of seed crystals were added, and after stirring for 2.0 h, 100.0 g of alkaline silica sol was added dropwise. After vigorously stirring at 50° C. for 3.0 h, 2.0 g of n-butanol was added to the solution, and after vigorously stirring for 2.0 h, a crystallized gel having the same composition as the raw material in Example 1 was obtained.

[0085] The crystallized gel was crystallized at 170°C for 42.0 h, and the product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain the original powder of the product.

[0086] The product prepared in this comparative example does not have the characteristic peak of the MFI structure molecular sieve structure.

[0087] By comparing Example 1 with Comparative Example 1, it can be seen that when methanol is the first template and alkaline silica sol is the silicon source, it is difficult to synthesize a high-crystallinity multi-level pore pure silicon Silicalite-1 molecular sieve product without sufficient pretreatment of the silicon source.

[0088] Comparative Example 2

[0089] This comparative example provides a method for preparing a molecular sieve, wherein the method comprises:

[0090] The silica sol was pretreated in the same manner as in Example 2 to obtain a pretreated silicon source mixed solution. 28.0 g of ethanol and 3.0 g of seed crystals were added to the pretreated silicon source mixed solution, the temperature was raised to 60°C and stirred for 2.0 h, 1.5 g of n-butanol was added dropwise, 1.2 g of sodium hydroxide particles were added after vigorous stirring for 1.0 h, and the crystallized gel was obtained after continuing to stir for 1.0 h at 170°C, crystallized for 45.0 h, and the crystallized product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain the product raw powder.

[0091] The XRD pattern of the product prepared in this comparative example is shown in Fig. 9 The intensity of the characteristic peak of MFI of the product is extremely low. The specific surface area of ​​the product is measured by BET (N2 adsorption), and its total specific surface area is 30.58.

[0092] Comparison of Example 2 with Comparative Example 2 shows that when ethanol is the first template and alkaline silica sol is the silicon source, even if the silicon source is pretreated and the feeding sequence is disrupted, a high-crystallinity multi-level pore pure silicon Silicalite-1 molecular sieve product cannot be synthesized.

[0093] Comparative Example 3

[0094] This comparative example provides a method for preparing a molecular sieve, wherein the method comprises:

[0095] No seed crystals were added during the pretreatment of the silicon source, and the remaining steps were the same as those in Example 4 to obtain a pretreated silicon source mixed solution.

[0096] 1.6 g of sodium hydroxide particles were added to the pretreated silicon source mixed solution, the mixture was stirred for 0.5 h and then heated to 50°C, 10.0 g of methanol was added, and 2.0 g of n-butanol was added dropwise after stirring for 1.0 h until the solution was clarified. After vigorous stirring for 2.0 h, 10.0 g of seed crystals were added to obtain a crystallized gel, which was then crystallized at 100°C for 20.0 h and then heated to 170°C for crystallization for 30.0 h. The crystallized product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain the product raw powder.

[0097] The XRD pattern of the product prepared in this comparative example is shown in Fig.10 The characteristic peak intensity of γ-SiO2 in the product XRD spectrum is relatively high, and the MFI intensity is extremely low. The specific surface area of ​​the product is measured by BET (N2 adsorption), and its total specific surface area is 55.5.

[0098] Comparison of Example 4 with Comparative Example 3 shows that when methanol is used as the first template and alkaline silica sol is used as the silicon source, a pure phase high crystallinity pure silicon MFI structure molecular sieve cannot be synthesized when the seed crystal does not participate in the crystallization gel mixing process.

[0099] Comparative Example 4

[0100] This comparative example provides a method for preparing a molecular sieve, wherein the method comprises:

[0101] The alkaline silica sol is pretreated in the same manner as in Example 6 to obtain a pretreated silicon source mixed solution;

[0102] To the pretreated silicon source mixture, 1.3 g of sodium hydroxide particles and 3.0 g of deionized water were added, the temperature was raised to 60°C after stirring for 0.5 h, 25.0 g of ethylene glycol and 2.0 g of n-butanol were added, and the mixture was stirred for 1.0 h to obtain a crystallized gel, which was crystallized at 170°C for 36.0 h. The product was washed, filtered, dried, and calcined at 550°C for 5.0 h to obtain the raw powder.

[0103] The MFI characteristic peak intensity of the product prepared in this comparative example is extremely low, and the specific surface area of ​​the product is measured by BET (N2 adsorption), and its total specific surface area is 113.5.

[0104] Comparing Example 6 with Comparative Example 4, it is shown that when ethylene glycol is used as the first template and alkaline silica sol is used as the silicon source, even if the silicon source is pretreated and the feeding order is the same, the feeding when the solution is not clarified due to insufficient stirring time still cannot synthesize a pure silicon MFI structure molecular sieve with high crystallinity.

[0105] The data of the products obtained in various embodiments and comparative examples are shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from Table 1, the present invention adopts different methods to pretreat the silicon source respectively, and strictly limits the material mixing order of the pretreated silicon source to obtain a crystallization mother liquor with uniform phase. Finally, low-carbon alcohol is successfully used as a template to synthesize a pure silicon Silicalite-1 molecular sieve product with good crystallinity and rich mesopores in a hydrothermal synthesis system. The product obtained by the present invention has high crystallinity and product yield, and can effectively reduce the production cost and environmental protection cost of the product, and has strong practical application significance.

Claims

1. A method for preparing multi-level pore pure silicon Silicalite-1 molecular sieve, wherein: The method includes: The silicon source is mixed with water, a first template agent, and a seed crystal, and stirred at 20-80° C. for 0.5-5 hours for pretreatment to obtain a pretreated silicon source mixed solution; wherein the first template agent includes at least one of methanol, ethanol, and ethylene glycol; The pretreated silicon source mixed solution is mixed with an alkali source, a seed crystal, and a first template, and after stirring at 20-80° C. for 1-5 hours, a second template is added and stirred for 1-10 hours to obtain a crystallized gel; wherein the second template comprises at least one of ethanol, ethylene glycol, and n-butanol; wherein the second template is of a different type from the first template; wherein the mass ratio of the pretreated silicon source mixed solution, the alkali source, the seed crystal, the first template, and the second template is: 1:(0.02-0.04):(0.05-0.15):(0.2-0.4):(0.05-0.15); The crystallized gel is crystallized at 150-180° C. for 10-72 hours to obtain a multi-level pore pure silicon Silicalite-1 molecular sieve.

2. The preparation method according to claim 1, wherein The seed crystals were prepared by the following method: Tetrapropylammonium hydroxide, ethyl orthosilicate and water in a molar ratio of 1TPAOH:(4.5-5.5)TEOS:(150-180)H2O are mixed and stirred for 8.0-12.0h, and then crystallized at 55-65°C for 45-50h, and then cooled to obtain a crystallized stock; the purified stock is mixed with water in a mass ratio of 1 crystallized stock:(8-12)H2O to obtain a seed crystal.

3. The preparation method according to claim 1, wherein The pretreatment temperature is 30-60°C; and / or In the process of preparing the crystallized gel, the pretreated silicon source mixed solution is mixed with the alkali source, the seed crystal and the first template, stirred at 30-70° C. for 1-5 hours, and then the second template is added and stirred for 1-10 hours to obtain the crystallized gel.

4. The preparation method according to claim 1, wherein During the preparation of the pretreated silicon source mixed solution, the silicon source is mixed with water, the first template and the seed crystals according to the mass feed ratio of 1SiO2: (0.1-0.5)H2O: (0.1-0.2) first template: (0.04-0.08) seed crystals.

5. The preparation method according to claim 1, wherein Mixing the silicon source with water, the first template, and the seed crystal comprises: Mix the silicon source with water, heat to 35-45°C, add seed crystals and stir for 0.5-1.5h, then add the first template dropwise.

6. The preparation method according to claim 1, wherein The first template comprises at least one of methanol and ethanol; and / or The second template is n-butanol; and / or The silicon source includes at least one of alkaline silica sol, neutral silica sol, acidic silica sol, white carbon black, solid silica gel and ethyl orthosilicate; The alkali source includes at least one of sodium hydroxide and potassium hydroxide.

7. The preparation method according to claim 1, wherein Mixing the pretreated silicon source mixed solution with the alkali source, the seed crystal, and the first template agent comprises: Add an alkali source to the pretreated silicon source mixture, stir for no more than 1.0 hour, then heat to 45-55° C., add a seed crystal, stir for 0.5-1.5 hours, then add the first template.

8. The preparation method according to claim 1, wherein The crystallization temperature is 160-175°C, and the crystallization time is 15-40h.

9. The preparation method according to claim 1, wherein The method also includes: washing, filtering, drying and roasting the crystallized product.

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