A method for rapidly synthesizing zsm-5 molecular sieve

Abstract

The application discloses a method for rapidly synthesizing ZSM-5 molecular sieve, which comprises the following steps: S1, mixing an aluminum source and deionized water to obtain a clear aluminum source solution, and stirring to obtain a clear solution A by adding an alkali source; S2, stirring the clear solution A at room temperature to form a gel after adding a silicon source, seeds, and crystallization promoters R1 and R2, and performing a crystallization reaction on the gel at 160-220 DEG C, and the crystallization time is 4-8 h; the promoter R1 is one or more of sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, and the promoter R2 is sodium tripolyphosphate and / or sodium hexametaphosphate; and S3, filtering and washing the crystallization product to neutral, and drying to obtain the ZSM-5 molecular sieve. In the synthesis process of the molecular sieve, no expensive organic template agent is added, but the seed and the crystallization promoter are used to promote the nucleation process of the molecular sieve, and provide a structure guiding effect for the growth of the molecular sieve.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve preparation technology, specifically relating to a method for rapidly synthesizing ZSM-5 molecular sieves. Background Technology

[0002] Molecular sieves are a class of crystalline materials with ordered pore structures. Since the first artificial synthesis of molecular sieves in the 1940s, based on the study of the synthesis conditions of natural zeolites, a large number of researchers have devoted themselves to the artificial synthesis of molecular sieves. In the past few decades, a large number of novel molecular sieves have been synthesized artificially. These molecular sieves have been widely used in catalytic cracking, alkylation, aromatization, methanol-to-olefins, tail gas denitrification, organic synthesis, and adsorption separation due to their excellent properties (such as high structural stability, excellent ion exchange and mass transfer capabilities, strong acidity, low production cost, and sieving capabilities brought about by their three-dimensional pore structure).

[0003] The most commonly used synthesis method for molecular sieves is the traditional hydrothermal method. The hydrothermal synthesis of zeolites mainly includes two processes: the formation of aluminosilicate hydrated gel and the crystallization of the hydrated gel. The entire synthesis process can be roughly summarized as follows: First, the initial raw materials such as silicon source, aluminum source, template agent, and alkali source are mixed at a specific temperature and dynamically stirred. After a period of time, the resulting gel is transferred to a sealed reaction vessel and placed in a high-temperature environment for crystallization. After that, the reaction vessel is removed and the product is separated from the liquid to obtain the zeolite molecular sieve. Current theories generally divide the crystallization process into four steps: (1) repolymerization of silicates and aluminates in different polymerization states; (2) zeolite nucleation process; (3) nucleus growth process; (4) growth of zeolite crystals and the secondary nucleation process that may be triggered. The advantages of the hydrothermal synthesis method are that the reactants are uniformly dissolved in the system, the reaction conditions are mild, and it is easy to use; the cost of reactants is low. However, the disadvantage of this method is that the required crystallization time is long. In order to further accelerate the crystallization process of molecular sieves, many researchers have tried to add various crystallization promoters to the initial gel to accelerate the synthesis process.

[0004] CN201911169395.7 discloses a method for rapidly synthesizing beta molecular sieves with controllable particle size. The method involves uniformly mixing a silicon source, an aluminum source, an inorganic base, a microporous template agent, deionized water, and a crystal particle size control agent R (imidazole, 2-methylimidazole, 2-chloroimidazole, or 2-aminoimidazole). After stirring, the mixture is directly crystallized at high temperature to obtain beta molecular sieves with particle sizes ranging from 50 nm to 3 μm. However, the added imidazole and imidazole compounds are toxic to humans and pose a hazard to the environment when dissolved in water, thus making them unsuitable for large-scale use. CN112897547B discloses a method for rapidly synthesizing aluminum-free Sn-Beta molecular sieves. The method involves mixing a silicon source with an organic template agent tetraethylammonium hydroxide, and then adding an alkali metal or alkaline earth metal salt (Li...) to the mixture.+ Na + K + Mg 2+ Ca 2+ Ba 2 + The process involves reacting chlorides, sulfates, nitrates, and acetates with a Sn source, stirring for a certain time, then adding hydrofluoric acid or ammonium fluoride as a mineralizing agent, followed by dealufted Beta or pure Si-Beta as seed crystals. After thorough mixing, the mixture is loaded into a molecular sieve crystallization vessel for rapid crystallization to obtain the product molecular sieve. Although this method can significantly alter the properties of the colloid during gelation by adding only a small amount of alkali metal or alkaline earth metal salts, promoting the polymerization of silicate species and thus shortening the crystallization time, the addition of fluoride promoters and organic templates during the synthesis process is environmentally unfriendly. Furthermore, the addition of organic templates increases the synthesis cost, hindering the widespread adoption of this technology. CN109987613B discloses a method for the rapid synthesis of pure silicon MCM-41 molecular sieves. The method uses hexadecyltrimethylammonium bromide (CTMAB) as a surfactant, which is combined with sodium hydroxide and water to form a solution. Sodium thiosulfate (Na₂S₂O₃) is added and mixed uniformly. H₂SO₄ is slowly added dropwise to adjust the pH of the solution to 8.5-10.0. A silicon source is then added to the solution to form a reactive sol. This reactive sol is crystallized at a temperature of 80-110℃ for 2-12 hours to obtain crystallized pure silicon MCM-41 molecular sieves. However, this invention uses an organic surfactant, which could cause environmental pollution during subsequent removal. CN115611294A discloses a rapid synthesis method for ZSM-48 molecular sieves. The method involves: S1, adding a mixed solution of template agent P, template agent Q, and water to a uniformly stirred mixture of aluminum source, alkali source, and water, followed by the addition of an aqueous solution of a crystallization inducing agent to form mixture A; S2, adding a mixture of a morphology modifier, a silicon source, and water to mixture A and stirring; S3, loading the mixture from S2 into an acid- and alkali-resistant sealed reactor, heating from 20°C to 120-180°C over 3-8 hours at a rotation speed of 30-80 rpm, and hydrothermally crystallizing for 10-120 hours. After filtration, washing, drying, and calcination, ZSM-48 molecular sieves are obtained. The drying conditions are: heating to 120°C in air for 2-4 hours; the calcination conditions are: heating to 550°C-600°C and calcining for 8-40 hours over 8 hours. This patent also utilizes organic surfactants.

[0005] Analysis of the aforementioned patents and existing technologies reveals that the addition of crystallization promoters promotes the formation of the crystalline phase structure of molecular sieves and can accelerate the crystallization of molecular sieves to a certain extent. However, these substances are usually organic compounds, which are generally expensive. Their addition increases the crystallization cost of molecular sieves, and they need to be removed in subsequent processes, which can pollute the environment. Therefore, they are not suitable for subsequent large-scale industrial production. Summary of the Invention

[0006] In view of the many problems existing in the prior art, the present invention aims to develop a method for rapid synthesis of ZSM-5 molecular sieves, which is green, low-cost, easy to operate, scalable, and significantly shortens the crystallization time.

[0007] To achieve the above objectives, the present invention provides a method for rapid synthesis of ZSM-5 molecular sieves, comprising the following steps:

[0008] S1, mix aluminum source and deionized water to obtain a clear aluminum source solution, then add alkali source and stir to obtain clear solution A;

[0009] S2, add silicon source and seed crystal to clear solution A, then add crystallization promoters R1 and R2, stir to form a gel, and crystallize the gel at 160-220℃ for 4-8 hours. Crystallization promoter R1 is one or more of sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, and crystallization promoter R2 is sodium tripolyphosphate and / or sodium hexametaphosphate.

[0010] S3. After filtering and washing the crystallized product to neutrality, it is dried to obtain ZSM-5 molecular sieve.

[0011] The method for rapid synthesis of ZSM-5 molecular sieves described in this invention has a molar ratio of aluminum source, silicon source, promoter R1, promoter R2, alkali source, and water of 1:30-200:0.3-4.5:0.3-3:4-8:500-2000, wherein the aluminum source, silicon source, and alkali source are calculated as oxides.

[0012] In the method for rapid synthesis of ZSM-5 molecular sieves described in this invention, when adding seed crystal promoters, promoter R1 is added first, followed by promoter R2.

[0013] The method for rapid synthesis of ZSM-5 molecular sieves described in this invention involves adding seed crystals at a rate of 1-10% of the total SiO2 mass in the system.

[0014] In the method for rapid synthesis of ZSM-5 molecular sieves described in this invention, the crystallization reaction in step S2 is carried out under oil bath conditions.

[0015] The method for rapid synthesis of ZSM-5 molecular sieves according to the present invention uses aluminum source as one or more of aluminum sulfate, aluminum chloride, aluminum hydroxide, sodium aluminate and boehmite.

[0016] The method for rapid synthesis of ZSM-5 molecular sieves according to the present invention uses sodium hydroxide and / or potassium hydroxide as the alkali source.

[0017] The method for rapid synthesis of ZSM-5 molecular sieves according to the present invention uses silicon source as one or more of silica sol, water glass, silica gel, sodium silicate, and tetraethyl orthosilicate.

[0018] The method for rapid synthesis of ZSM-5 molecular sieves according to the present invention uses one or more of Silicalite-1, ZSM-5 and ZSM-11 molecular sieves as seed crystals.

[0019] Beneficial effects of this invention:

[0020] Instead of using expensive organic templates, seed crystals and crystallization promoters are employed in the synthesis of molecular sieves to facilitate nucleation and provide structure guidance for growth. The crystallization promoters consist of an inorganic alkali metal salt R1 and a dispersant R2. R1 promotes the formation of five-membered ring secondary structural units in the gel solid phase and facilitates nucleation and crystallization by promoting the condensation and rearrangement of these units. By adding R1 first and then R2, R2 disperses and homogenizes the aluminosilicate gel formed by R1 and other materials, reducing aluminosilicate aggregation and promoting uniformity of subsequent gel nucleation. This increases the growth sites for molecular sieve crystals and shortens the crystallization time. Since the system does not contain expensive organic templates or surfactants, the environmental pollution caused by calcining templates is eliminated, and the synthesis cost is reduced. Attached Figure Description

[0021] Figure 1 These are the XRD patterns of the ZSM-5 molecular sieves synthesized in Examples 1-9.

[0022] Figure 2 This is a SEM image of the ZSM-5 molecular sieve synthesized in Example 1.

[0023] Figure 3 This is a comparison of XRD patterns of ZSM-5 molecular sieves synthesized in Example 3 and Comparative Examples 1 and 2. Detailed Implementation

[0024] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0025] Raw material source:

[0026] 1) Sodium hydroxide, analytical grade, Shanghai Test Equipment Group

[0027] 2) Potassium hydroxide, analytical grade, Shanghai Test Equipment Group

[0028] 3) Boehmite, industrial grade, sourced from Lanzhou Petrochemical Company Catalyst Plant.

[0029] 4) Aluminum sulfate octahydrate, analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0030] 5) Aluminum hydroxide, analytical grade, Shanghai Maclean Biochemical Technology Co., Ltd.

[0031] 6) Sodium chloride, analytical grade, Shanghai Test Equipment Group

[0032] 7) Anhydrous sodium sulfate, analytical grade, Shanghai Test Equipment Group

[0033] 8) Potassium chloride, analytical grade, Shanghai Test Equipment Group

[0034] 9) Potassium sulfate, analytical grade, Shanghai Test Equipment Group

[0035] 10) Sodium tripolyphosphate, industrial grade, Qingzhou Yibai Chemical Co., Ltd.

[0036] 11) Sodium hexametaphosphate, industrial grade, Hebei Migomei Chemical Technology Co., Ltd.

[0037] 12) Sodium hypophosphite, analytical grade, Changshu Xinte Chemical Co., Ltd.

[0038] 13) Silica gel, industrial product, sourced from Lanzhou Petrochemical Company Catalyst Plant.

[0039] 14) Silica sol, industrial product, Shandong Chengshun Chemical Technology Co., Ltd.

[0040] 15) Ethyl orthosilicate, analytical grade, Beijing Innocare Technology Co., Ltd.

[0041] 16) ZSM-5 molecular sieve, purchased from Nankai Catalyst Factory

[0042] 17) ZSM-11 molecular sieve, Tianjin Delta Technology Co., Ltd.

[0043] 18) Silicalite-1 molecular sieve, Nankai Catalyst Factory

[0044] Specific analysis methods:

[0045] The crystallinity of the molecular sieve was determined by X-ray diffraction using a D / max-3C X-ray powder diffractometer manufactured by Rigaku Corporation, Japan. The pore size distribution of the samples was determined using an Autosorb-3B specific surface area analyzer manufactured by Quantachrome Corporation, USA, through a low-temperature (77.3K) N2 adsorption-desorption experiment. Specific implementation examples:

[0047] Examples 1 to 9 illustrate methods for synthesizing molecular sieves.

[0048] Example 1

[0049] Add 3.24 g of boehmite to 200 g of deionized water and stir dynamically for 5 minutes. After the boehmite is completely dissolved, add 6.84 g of sodium hydroxide and continue stirring for 5 minutes. Then slowly add 44 g of powdered silica gel and 0.4 g of ZSM-5 molecular sieve seed crystals, and simultaneously add 0.39 g of sodium chloride and stir for 5 minutes. Finally, add 2.54 g of sodium tripolyphosphate and stir the resulting gel at room temperature for 1.5 hours. Crystallize the gel at 160 °C for 8 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120 °C to obtain ZSM-5 molecular sieve.

[0050] Example 2

[0051] Add 0.4 g of boehmite to 100 g of deionized water and stir dynamically for 10 minutes. After the boehmite is completely dissolved, add 2.13 g of sodium hydroxide and continue stirring for 15 minutes. Then slowly add 34 g of powdered silica gel and 3.3 g of silicalite-1 molecular sieve seed crystals, and simultaneously add 0.73 g of sodium chloride and stir for 5 minutes. Finally, add 2.95 g of sodium tripolyphosphate and stir the resulting gel at room temperature for 2.5 hours. Crystallize the gel at 220°C for 4 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120°C to obtain ZSM-5 molecular sieve.

[0052] Example 3

[0053] Add 2.4 g of aluminum sulfate octadechydrate to 110 g of deionized water and stir dynamically for 15 minutes. After the aluminum sulfate octadechydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seed crystals, and simultaneously add 1 g of sodium chloride and stir for 5 minutes. Finally, add 2.1 g of sodium tripolyphosphate and stir the formed gel at room temperature for 2 hours. Crystallize the gel at 180 °C for 6 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120 °C to obtain ZSM-5 molecular sieve.

[0054] Example 4

[0055] Add 1.6 g of aluminum sulfate octadechydrate to 40 g of deionized water and stir dynamically for 15 minutes. After the aluminum sulfate octadechydrate is completely dissolved, add 2.8 g of potassium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 50 g of silica sol and 0.5 g of ZSM-5 molecular sieve seed crystals, and simultaneously add 0.4 g of potassium chloride and stir for 5 minutes. Finally, add 2.4 g of sodium hexametaphosphate and stir the formed gel at room temperature for 3 hours. Crystallize the gel at 180°C for 6 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120°C to obtain ZSM-5 molecular sieve.

[0056] Example 5

[0057] Add 2.1 g of aluminum hydroxide to 200 g of deionized water and stir dynamically for 15 minutes. After the aluminum hydroxide is completely dissolved, add 6 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 149.76 g of tetraethyl orthosilicate and 2 g of ZSM-5 molecular sieve seed crystals, and simultaneously add 1.2 g of sodium chloride and stir for 10 minutes. Finally, add 8 g of sodium hexametaphosphate and stir the formed gel at room temperature for 3 hours. Crystallize the gel at 180°C for 7 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120°C to obtain ZSM-5 molecular sieve.

[0058] Example 6

[0059] Add 2.1 g of aluminum hydroxide to 200 g of deionized water and stir dynamically for 15 minutes. After the aluminum hydroxide is completely dissolved, add 6 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 130 g of tetraethyl orthosilicate and 2 g of ZSM-5 molecular sieve seed crystals, and simultaneously add 0.6 g of sodium chloride and stir for 10 minutes. Finally, add 4 g of sodium tripolyphosphate and stir the formed gel at room temperature for 1.5 hours. Crystallize the gel at 180°C for 8 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120°C to obtain ZSM-5 molecular sieve.

[0060] Example 7

[0061] Add 1.2 g of aluminum sulfate octadechydrate to 55 g of deionized water and stir dynamically for 10 minutes. After the aluminum sulfate octadechydrate is completely dissolved, add 4 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 45 g of silica sol and 0.75 g of silicalite-1 molecular sieve seed crystals, and simultaneously add 0.61 g of anhydrous sodium sulfate and stir for 5 minutes. Finally, add 1.05 g of sodium tripolyphosphate and stir the formed gel at room temperature for 2 hours. Crystallize the gel at 180 °C for 6 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120 °C to obtain ZSM-5 molecular sieve.

[0062] Example 8

[0063] Add 3.2 g of aluminum sulfate octadecahydrate to 80 g of deionized water and stir dynamically for 10 minutes. After the aluminum sulfate octadecahydrate is completely dissolved, add 5.6 g of potassium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 100 g of silica sol and 1 g of ZSM-5 molecular sieve seed crystals, and simultaneously add 0.94 g of potassium chloride and stir for 5 minutes. Finally, add 4.8 g of sodium hexametaphosphate and stir the formed gel at room temperature for 3 hours. Crystallize the gel at 180 °C for 6 hours. Filter and wash the crystallization solution until neutral, and then dry the filter cake overnight at 120 °C to obtain ZSM-5 molecular sieve.

[0064] Example 9

[0065] The difference from Example 3 is that sodium tripolyphosphate is added first, followed by sodium chloride.

[0066] Add 2.4 g of aluminum sulfate octadecahydrate to 110 g of deionized water and stir dynamically for 15 minutes. After the aluminum sulfate octadecahydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seed crystals, and simultaneously add 2.1 g of sodium tripolyphosphate and stir for 5 minutes. Finally, add 1 g of sodium chloride and stir the formed gel at room temperature for 2 hours. Crystallize the gel at 180 °C for 6 hours. Filter and wash the crystallization solution until neutral, and dry the filter cake overnight at 120 °C to obtain ZSM-5 molecular sieve.

[0067] Comparative Example 1

[0068] The difference from Example 3 is that sodium chloride is not added during the crystallization process.

[0069] Add 2.4 g of aluminum sulfate octadechydrate to 110 g of deionized water and stir dynamically for 15 minutes. After the aluminum sulfate octadechydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seed crystals and stir for 5 minutes. Finally, add 2.1 g of sodium tripolyphosphate and stir the formed gel at room temperature for 2 hours. Crystallize the gel at 180°C for 6 hours. Filter and wash the crystallization solution until neutral, and dry the filter cake overnight at 120°C to obtain ZSM-5 molecular sieve.

[0070] Comparative Example 2

[0071] The difference from Example 3 is that sodium tripolyphosphate was not added as a crystallization accelerator during the synthesis process; instead, sodium hypophosphite was used as the crystallization accelerator.

[0072] Add 2.4 g of aluminum sulfate octadecahydrate to 110 g of deionized water and stir dynamically for 15 minutes. After the aluminum sulfate octadecahydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seed crystals, and simultaneously add 1 g of sodium chloride and stir for 5 minutes. Finally, add 3.02 g of sodium hypophosphite and stir the formed gel at room temperature for 2 hours. Crystallize the gel at 180 °C for 6 hours. Filter and wash the crystallization solution until neutral, and dry the filter cake overnight at 120 °C to obtain ZSM-5 molecular sieve.

[0073] Table 1 shows that the molecular sieve obtained using this invention has higher crystallinity, specific surface area and pore volume, and shorter crystallization time. It also shows that in order to achieve rapid synthesis and crystallization, crystallization promoters R1 and R2 need to be used in combination in a certain order. Using R1 alone or replacing R2 with other promoters cannot achieve the effect described in this invention.

[0074] Table 1. Specific surface area and pore volume of molecular sieves

[0075]

[0076]

[0077] This invention may have other embodiments. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of this invention.

Claims

1. A method for rapid synthesis of ZSM-5 molecular sieves, characterized in that, Includes the following steps: S1, mix aluminum source and deionized water to obtain a clear aluminum source solution, then add alkali source and stir to obtain clear solution A; S2, add silicon source and seed crystal to clear solution A, then add crystallization promoters R1 and R2, stir to form a gel, and crystallize the gel at 160-220℃ for 4-8 hours. Crystallization promoter R1 is one or more of sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, and crystallization promoter R2 is sodium tripolyphosphate and / or sodium hexametaphosphate. S3. The crystallized product was filtered, washed until neutral, and then dried to obtain ZSM-5 molecular sieve.

2. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, The molar ratio of aluminum source, silicon source, accelerator R1, accelerator R2, alkali source, and water is 1:30~200:0.3~4.5:0.3~3:4~8:500~2000, wherein the aluminum source, silicon source, and alkali source are calculated as oxides.

3. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, When adding seed crystal promoters, add promoter R1 first, then add promoter R2.

4. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, The amount of seed crystals added is 1 to 10% of the total SiO2 mass in the system.

5. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, The crystallization reaction in step S2 is carried out under oil bath conditions.

6. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, The aluminum source is one or more of aluminum sulfate, aluminum chloride, aluminum hydroxide, sodium aluminate, and boehmite.

7. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, The alkali source is sodium hydroxide and / or potassium hydroxide.

8. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, The silicon source is one or more of silica sol, water glass, silica gel, sodium silicate, and tetraethyl orthosilicate.

9. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that, The seed crystals are one or more of Silicalite-1, ZSM-5 and ZSM-11 molecular sieves.

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