Synthesis method of Beta-coated ZSM-12 molecular sieve with core-shell structure and synthesized molecular sieve

Abstract

The invention discloses a synthesis method of a Beta (at) ZSM-12 molecular sieve with a core-shell structure and the synthesized molecular sieve. Comprising the following steps: (1) mixing a Beta molecular sieve core, a template agent and water to obtain a mixture A, and aging; (2) mixing a silicon source, an aluminum source, an alkali source and water to obtain a mixture B; and (3) mixing the mixture A and the mixture B, crystallizing in a closed reactor, washing, separating and drying to obtain the molecular sieve. The synthesis method provided by the invention breaks through the bottleneck that a core-shell structure is difficult to synthesize. Through aging, the molecular sieve core and the template agent are better combined, and crystallization of the core-shell structure is promoted; by changing synthesis parameters, molecular sieves with different ZSM-12 molecular sieve proportions can be prepared, the core-shell proportion can be adjusted according to reaction requirements, and the ZSM-12 molecular sieve has potential application prospects in many reaction processes.

Description

Technical Field

[0001] The present application relates to a method for synthesizing a Beta@ZSM-12 molecular sieve with a core-shell structure and the molecular sieve synthesized therefrom, and belongs to the field of molecular sieve synthesis. Background Art

[0002] Beta molecular sieve is a microporous molecular sieve with a three-dimensional twelve-membered ring pore system (0.76nm×0.67nm), and ZSM-12 molecular sieve is a microporous molecular sieve with a one-dimensional twelve-membered ring straight pore structure (0.57nm×0.61nm). Beta and ZSM-12 molecular sieves show their own characteristics in the reaction process of petrochemicals. The acidity of Beta molecular sieve is adjustable, and the larger pore size is conducive to the related reactions with macromolecules as raw materials, showing a higher raw material conversion rate and reaction stability; ZSM-12 molecular sieve is usually a high silicon-aluminum ratio molecular sieve, which leads to a low raw material conversion rate in the related reaction process, but because of its unique one-dimensional straight pore structure, it shows excellent shape selectivity in many reactions. Therefore, Beta molecular sieve is used as the core and ZSM-12 molecular sieve is used as the shell, and the advantages of both are fully combined to prepare a core-shell structure molecular sieve, hoping to show unique shape selectivity in specific reactions.

[0003] However, the synthesis of Beta@ZSM-12 molecular sieve with core-shell structure is difficult, and there is no effective synthesis strategy so far. There are only reports on the synthesis methods of related eutectic or mixed crystal Beta / ZSM-12 molecular sieves. Patent CN110451519B reports a eutectic material containing ZSM-12 structure and its preparation method. The eutectic material prepared by the segmented crystallization method includes 1.2% to 98% of ZSM-12 structural materials, and the rest is MOR or Beta material. Patent CN106587094B uses solvent evaporation method to prepare block Beta-ZSM-12 symbiotic molecular sieve with a particle size of 2 to 4μm. The electron microscope image shows nano-scale particles attached to the surface of cubic block crystals. Patent CN104591217B provides a Beta / ZSM-12 composite molecular sieve and its synthesis method, which requires pre-ultrasonic treatment of ZSM-12 molecular sieve with glucose as a seed before synthesis. However, the several eutectics or composite products reported above are all in a physical mixed state, the interaction between the two molecular sieves is weak, and no core-shell structure is formed. Summary of the invention

[0004] The purpose of this application is to develop a method for synthesizing a Beta@ZSM-12 molecular sieve with a core-shell structure. This method promotes the crystallization of the Beta@ZSM-12 molecular sieve with a core-shell structure by preparing a mixed solution of a molecular sieve core and a template agent for aging. In addition, by changing the synthesis parameters, the synthesis of Beta@ZSM-12 molecular sieves with different ZSM-12 molecular sieve ratios can be regulated.

[0005] According to one aspect of the present application, a method for synthesizing a Beta@ZSM-12 molecular sieve with a core-shell structure is provided, comprising the following steps:

[0006] (1) mixing a Beta molecular sieve core, a template and water to obtain a mixture A, and aging the mixture;

[0007] (2) mixing a silicon source, an aluminum source, an alkali source and water to obtain a mixture B;

[0008] (3) Mixing the mixture A and the mixture B, crystallizing in a closed reactor, washing, separating, and drying to obtain the Beta@ZSM-12 molecular sieve with a core-shell structure.

[0009] The Beta molecular sieve core is a Beta molecular sieve with a *BEA topological structure;

[0010] The template agent is a template agent for preparing ZSM-12 molecular sieve and is selected from at least one of tetraethylammonium hydroxide, tetraethylammonium chloride, tetraethylammonium bromide, methyltriethylammonium hydroxide and methyltriethylammonium chloride;

[0011] The silicon source is selected from at least one of solid silica gel, white carbon black and silica sol;

[0012] The aluminum source is selected from at least one of sodium aluminate, pseudo-boehmite, aluminum chloride or aluminum sulfate;

[0013] The alkali source is selected from at least one of sodium hydroxide and potassium hydroxide.

[0014] The mass of the Beta molecular sieve core is 0.1 to 50 wt% of the mass of the silicon source;

[0015] The molar ratio of the template to the silicon source is 0.05 to 1;

[0016] The molar ratio of the silicon source to the aluminum source is 20 to 500;

[0017] The molar ratio of the alkali source to the silicon source is 0.01 to 0.25;

[0018] The molar ratio of the total amount of water to the silicon source is 10 to 30;

[0019] The water in mixture A is sufficient to ensure that the template can be completely dissolved, and the remaining water is the water in mixture B.

[0020] The molar amount of the silicon source is calculated as the molar amount of silicon oxide (SiO2) therein, the molar amount of the aluminum source is calculated as the molar amount of aluminum oxide (Al2O3) therein, and the molar amount of the alkali source is calculated as the molar amount of Na2O and / or K2O.

[0021] The aging temperature is 40-100°C;

[0022] The aging time is 2 to 24 hours.

[0023] The crystallization temperature is 120-160°C;

[0024] The crystallization time is 24 to 120 hours.

[0025] According to another aspect of the present application, a core-shell structured Beta@ZSM-12 molecular sieve is provided, which is prepared by the above-mentioned synthesis method;

[0026] The Beta@ZSM-12 molecular sieve with a core-shell structure has a Beta molecular sieve as a core and a ZSM-12 molecular sieve as a shell.

[0027] The mass fraction of the ZSM-12 molecular sieve as a shell in the Beta@ZSM-12 molecular sieve with a core-shell structure is 10 to 95 wt %.

[0028] The core-shell structured Beta@ZSM-12 molecular sieve is a sodium-type / potassium-type molecular sieve, and the hydrogen-type Beta@ZSM-12 molecular sieve can be obtained by calcination and ion exchange, or the functionalized Beta@ZSM-12 molecular sieve can be obtained by other post-treatment methods.

[0029] The beneficial effects of this application include:

[0030] The synthesis method of the core-shell structured Beta@ZSM-12 molecular sieve proposed in this application breaks through the bottleneck that the core-shell structure is difficult to synthesize. By preparing a mixed solution of the Beta molecular sieve core and the template agent and aging it, the molecular sieve core and the template agent have better binding force, which promotes the crystallization of the core-shell structured Beta@ZSM-12 molecular sieve; in addition, by changing the synthesis parameters, Beta@ZSM-12 molecular sieves with different ZSM-12 molecular sieve ratios can be prepared, and the core-shell ratio can be adjusted according to the reaction requirements, which has potential application prospects in many reaction processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The following are X-ray diffraction (XRD) spectra of the products in various embodiments.

[0032] Figure 2 This is a scanning electron microscope (SEM) image of the product of Example 1, with a scale of 100 nm.

[0033] Figure 3 This is a scanning electron microscope (SEM) image of the product of Comparative Example 1, with a scale of 2 μm.

[0034] Figure 4This is a scanning electron microscope (SEM) image of the Beta molecular sieve core, with a scale of 2μm. DETAILED DESCRIPTION

[0035] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0036] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0037] Example 1

[0038] First, 11.8g of Beta molecular sieve core (85% on dry basis), 76.6g of methyltriethylammonium chloride (99%) and 150g of water are mixed as solution A and aged at 60°C for 12h. Then, 2.2g of sodium hydroxide, 2.0g of solid sodium aluminate (49% Al2O3, 38% Na2O), 196.1g of silica sol (30.6% SiO2, 0.32% Na2O, 0.02% Al2O3) and 133.9g of water are mixed as solution B. Solutions A and B are mixed evenly, crystallized at 150°C in a stainless steel reactor for 120h, and then washed, separated and dried to obtain the core-shell structured Beta@ZSM-12 molecular sieve. The molar ratio of the synthetic raw materials is: 0.05Na2O: 0.01Al2O3: 1.0SiO2: 0.5MTEACl: 25H2O, and the mass of the Beta molecular sieve core is 16.6% of the mass of the silicon source.

[0039] The X-ray diffraction (XRD) spectrum of the product of Example 1 is as follows Figure 1 shown.

[0040] Figure 2 This is a scanning electron microscope (SEM) image of the product of Example 1.

[0041] like Figure 1 As shown, the X-ray diffraction (XRD) spectrum of the product of this example shows that it contains characteristic diffraction peaks of Beta and ZSM-12 molecular sieves. By calculation, the mass percentage of ZSM-12 molecular sieve is 80%. Figure 2 As shown, the product of this example is spindle-shaped crystals.

[0042] Comparative Example 1

[0043] The synthetic molar ratio and the mass ratio of the Beta molecular sieve core to the silicon source are the same as those in Example 1. There is no aging process, and the reaction raw materials are directly mixed. 11.8g Beta molecular sieve, 76.6g methyltriethylammonium chloride, 2.2g sodium hydroxide, 2.0g solid sodium metaaluminate, 196.9g silica sol and 133.9g water are directly mixed evenly, crystallized in a stainless steel reactor at 150°C for 120h, and then washed, separated and dried to obtain the product. Figure 1 As shown, the X-ray diffraction (XRD) spectrum of the product of this example is similar to that of Example 1, and contains characteristic diffraction peaks of Beta and ZSM-12 molecular sieves. However, the scanning electron microscope image ( Figure 3 ) shows that it contains spindle-shaped crystals and nanoparticle crystals, among which the morphology of the nanoparticle crystals is similar to that of the Beta molecular sieve core ( Figure 4 ), which proves that the product is in the state of two phases separated: Beta and ZSM-12.

[0044] Example 2

[0045] First, 0.07g of Beta molecular sieve core, 61.3g of methyltriethylammonium chloride and 150g of water were mixed as solution A, and aged at 40°C for 24h. Then, 6.2g of sodium hydroxide, 2.0g of solid sodium metaaluminate, 196.1g of silica sol and 187.9g of water were mixed as solution B. Solutions A and B were mixed evenly, crystallized in a stainless steel reactor at 150°C for 120h, and then washed, separated and dried to obtain the core-shell structured Beta@ZSM-12 molecular sieve. The molar ratio of the synthetic raw materials is: 0.1Na2O: 0.01Al2O3: 1.0SiO2: 0.4MTEACl: 30H2O, and the mass of the Beta molecular sieve core is 0.1% of the mass of the silicon source.

[0046] The X-ray diffraction (XRD) spectrum of the product of this example is as follows: Figure 1 As shown in FIG. 1 , the mass percentage of ZSM-12 molecular sieve is 95% by calculation.

[0047] Example 3

[0048] First, 14.1g of Beta molecular sieve core, 117.6g of tetraethylammonium hydroxide solution (25% aqueous solution) and 20g of water are mixed as solution A, and then aged at 100°C for 6h. Then, 19.2g of sodium hydroxide, 6.7g of pseudo-boehmite (75%), 196.1g of silica sol and 31.8g of water are mixed as solution B. Solutions A and B are mixed evenly, crystallized in a stainless steel reactor at 160°C for 48h, and then washed, separated and dried to obtain the core-shell structured Beta@ZSM-12 molecular sieve. The molar ratio of the synthetic raw materials is: 0.25Na2O: 0.05Al2O3: 1.0SiO2: 0.2TEAOH: 25H2O, and the mass of the Beta molecular sieve core is 20% of the mass of the silicon source.

[0049] The X-ray diffraction (XRD) spectrum of the product of this example is as follows: Figure 1 As shown in FIG. 1 , the mass percentage of ZSM-12 molecular sieve is 72% by calculation.

[0050] Example 4

[0051] First, 17.6g of Beta molecular sieve core, 33.1g of tetraethylammonium chloride solution and 50g of water are mixed as solution A, and then aged at 80°C for 12h. Then, 1.1g of potassium hydroxide, 0.5g of aluminum chloride (99%), 68.9g of silica gel (87% on dry basis) and 86.1g of water are mixed as solution B. Solutions A and B are mixed evenly, and crystallized in a stainless steel reactor at 140°C for 96h. Then, the core-shell structured Beta@ZSM-12 molecular sieve is obtained by washing, separation and drying. The molar ratio of the synthetic raw materials is: 0.01K2O: 0.002Al2O3: 1.0SiO2: 0.05TEACl: 10H2O, and the mass of the Beta molecular sieve core is 25% of the mass of the silicon source.

[0052] The X-ray diffraction (XRD) spectrum of the product of this example is as follows: Figure 1 As shown in FIG. 1 , the mass percentage of ZSM-12 molecular sieve is 65% by calculation.

[0053] Example 5

[0054] First, 35.3g of Beta molecular sieve core, 42.0g of tetraethylammonium bromide solution (25% aqueous solution) and 50g of water are mixed as solution A, and then aged at 80°C for 12h. Then, 1.1g of potassium hydroxide, 3.4g of aluminum sulfate (99%), 63.2g of white carbon black (dry basis 95%) and 85.3g of water are mixed as solution B. Solutions A and B are mixed evenly, crystallized in a stainless steel reactor at 120°C for 168h, and then washed, separated and dried to obtain the core-shell structured Beta@ZSM-12 molecular sieve. The molar ratio of the synthetic raw materials is: 0.01K2O: 0.01Al2O3: 1.0SiO2: 0.05TEABr: 10H2O, and the mass of the Beta molecular sieve core is 50% of the mass of the silicon source.

[0055] The X-ray diffraction (XRD) spectrum of the product of this example is as follows: Figure 1 As shown in FIG. 1 , the mass percentage of ZSM-12 molecular sieve is 10% by calculation.

[0056] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for synthesizing a core-shell structured Beta@ZSM-12 molecular sieve, characterized in that: The following steps are involved: (1) mixing a Beta molecular sieve core, a template and water to obtain a mixture A, and aging the mixture; (2) mixing a silicon source, an aluminum source, an alkali source and water to obtain a mixture B; (3) Mixing the mixture A and the mixture B, crystallizing in a closed reactor, washing, separating, and drying to obtain the Beta@ZSM-12 molecular sieve with a core-shell structure.

2. The synthesis method according to claim 1, characterized in that The Beta molecular sieve core is a Beta molecular sieve with a *BEA topological structure; The template agent is selected from at least one of tetraethylammonium hydroxide, tetraethylammonium chloride, tetraethylammonium bromide, methyltriethylammonium hydroxide and methyltriethylammonium chloride; The silicon source is selected from at least one of solid silica gel, white carbon black and silica sol; The aluminum source is selected from at least one of sodium aluminate, pseudo-boehmite, aluminum chloride or aluminum sulfate; The alkali source is selected from at least one of sodium hydroxide and potassium hydroxide.

3. The synthesis method according to claim 1, characterized in that The mass of the Beta molecular sieve core is 0.1 to 50 wt% of the mass of the silicon source; The molar ratio of the template to the silicon source is 0.05 to 1; The molar ratio of the silicon source to the aluminum source is 20 to 500; The molar ratio of the alkali source to the silicon source is 0.01 to 0.25; The molar ratio of the total amount of water to the silicon source is 10 to 30; The molar amount of the silicon source is calculated as the molar amount of silicon oxide (SiO2) therein, the molar amount of the aluminum source is calculated as the molar amount of aluminum oxide (Al2O3) therein, and the molar amount of the alkali source is calculated as the molar amount of Na2O and / or K2O.

4. The synthesis method according to claim 1, characterized in that The aging temperature is 40-100°C; The aging time is 2 to 24 hours.

5. The synthesis method according to claim 1, characterized in that The crystallization temperature is 120-160°C; The crystallization time is 24 to 120 hours.

6. A Beta@ZSM-12 molecular sieve with a core-shell structure, characterized in that: Prepared by the synthesis method according to any one of claims 1 to 5; The Beta@ZSM-12 molecular sieve with a core-shell structure has a Beta molecular sieve as a core and a ZSM-12 molecular sieve as a shell.

7. The Beta@ZSM-12 molecular sieve with a core-shell structure according to claim 6, characterized in that: The mass fraction of the ZSM-12 molecular sieve as a shell in the Beta@ZSM-12 molecular sieve with a core-shell structure is 10 to 95 wt %.

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