A zsm-5@silicalite-1 core-shell molecular sieve, a preparation method and application thereof
By employing a seed-guided silicon source slow-release synthesis strategy, the acid site distribution of the ZSM-5@Silicalite-1 core-shell material was modulated, solving the problem of uncontrollable acid site distribution in existing technologies. This enabled the preparation of a highly efficient and low-cost catalyst suitable for reactions of aromatic compounds and low-carbon compounds.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DALIAN INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2024-12-03
- Publication Date
- 2026-06-05
AI Technical Summary
The acid site distribution of the existing ZSM-5@Silicalite-1 core-shell material is untunable, resulting in insufficient catalyst stability and shape selectivity, high preparation cost and poor reproducibility, making it difficult to apply on a large scale in industry.
By employing a seed-guided silicon source slow-release synthesis strategy, the content and size of Silicalite-1 seed crystals are simultaneously modulated to achieve precise modulation of the acid site distribution in the core-shell material, simplifying the preparation process and reducing costs.
The acid site distribution of the ZSM-5@Silicalite-1 core-shell material was made tunable, which improved the stability and shape selectivity of the catalyst, reduced the preparation cost, and increased the yield and reproducibility of a single batch, making it suitable for industrial scale-up production.
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Abstract
Description
Technical Field
[0001] This application relates to a ZSM-5@Silicalite-1 core-shell molecular sieve, its preparation method, and its application, belonging to the field of molecular sieves. Background Technology
[0002] Para-disubstituted alkylbenzenes (para-methylethylbenzene, diethylbenzene, xylene, etc.) are key polymerization monomers, mainly used in the production of specialty coatings, high-end resins, high-performance rubbers, and new plastics. Currently, they are primarily obtained through aromatic extraction and C9 aromatic separation processes during petroleum refining. The production of para-substituted methylethylbenzene, diethylbenzene, and xylene via alkylation reactions using toluene, ethylbenzene, benzene, methanol, and ethylene as raw materials is advantageous due to the wide availability of reactants and reduced dependence on petroleum feedstocks, making it of significant research value. Alkylation is a typical acid-catalyzed process. Traditional alkylation catalysts are homogeneous acid catalysts such as AlCl3 and H2SO4, but acidic molecular sieve-based catalytic materials have gradually emerged. ZSM-5 zeolite exhibits high activity in gas-phase alkylation reactions such as toluene-ethylene, toluene-methanol, and ethylbenzene-ethylene. However, the products are typically a thermodynamic mixture of three isomers, making product separation difficult. ZSM-5 molecular sieve has intersecting ten-membered ring channels. The sinusoidal channels parallel to the
[100] direction have a size of 0.51 nm × 0.55 nm, and the straight channels parallel to the
[010] direction have a size of 0.53 nm × 0.56 nm. Its channel size is smaller than that of meta- and ortho-substituted ethylbenzene, xylene, and diethylbenzene, resulting in limited diffusion of these substances within the ten-membered ring channels of the ZSM-5 molecular sieve. This indicates that the ten-membered ring channels have a sieving effect on molecules. However, due to the presence of numerous acidic sites at the pore openings and on the outer surface of the molecular sieve, these acidic sites lack shape selectivity. Consequently, the highly para-selective products diffused from the channels are prone to isomerization reactions on the surface, ultimately yielding a thermodynamic mixture of the three isomers.
[0003] Passivating the acidic sites on the outer surface of ZSM-5 catalyst is key to improving its para-selectivity. While complex multi-step modification methods can cover these acidic sites and improve para-selectivity, they are costly and have poor reproducibility. However, coating the surface of ZSM-5 with pure silica MFI zeolite (Silicalite-1) to prepare the ZSM-5@Silicalite-1 core-shell material effectively passivates the acidic sites, resulting in very high para-selectivity.
[0004] However, traditional methods for synthesizing ZSM-5 / Silicalite-1 core-shell materials face numerous challenges, including high preparation costs, high requirements for the quality of ZSM-5 crystal nuclei, extremely low single-reactor yields, poor product reproducibility, and extremely high requirements for silicon sources, thus limiting their large-scale industrial production. Bouzi Y et al. [Chem Mater, 2006, 18(20): 4959-4966] required numerous steps in preparing core-shell molecular sieves using a secondary growth method, including nanocrystal synthesis, nucleus pretreatment, nanocrystal adhesion, shell synthesis, calcination, and crystallization, which greatly reduced work efficiency. Although the synthesis method described in US20140256538 can obtain core / shell molecular sieves with better shell coverage, it involves many steps. Jeffrey D. Rimer et al. [ACS Nano, 2015, 9(4): 4006-4016] reported the synthesis of ZSM-5 / Silicalite-1 core-shell molecular sieves. First, ZSM-5 seed crystals were synthesized and then added to the mother liquor for synthesizing Silicalite-1, ultimately crystallizing to obtain the core-shell material. However, to avoid the silicon source forming nuclei independently under the guidance of the template agent during the coating process, the water-to-silicon ratio of the solution was greater than 200, leading to the generation of a large amount of organic wastewater during the preparation process. Furthermore, the core-shell material required ammonium exchange. Patent CN104556130A reported a gas-phase method for synthesizing ZSM-5 / Silicalite-1 core-shell materials. This method requires evaporating a considerable amount of water for synthesis, resulting in high energy consumption, and still requires the addition of ZSM-5 nuclei. Patent CN102671694A also reports a ZSM-5 / Silicalite-1 core-shell molecular sieve, its preparation method, and applications. However, its preparation process still requires the addition of ZSM-5 nuclei and ammonium exchange, resulting in imperfect coating and a para-selectivity below 85%. Patent CN104556131A reports a microwave-assisted synthesis of ZSM-5 / Silicalite-1 core-shell molecular sieves. This process requires the addition of ZSM-5 nuclei and the introduction of inorganic bases such as NaOH during coating, necessitating ammonium exchange of the resulting core-shell material. Furthermore, the large-scale application of microwave-assisted synthesis still faces significant challenges. To further improve the coating effect, patent CN107758689A uses silicon-treated ZSM-5 as the nucleus to microwave-assistedly coat the Silicalite-1 shell, making the coating process even more complex. Patent CN105268472A addresses the challenge of conventional core-shell molecular sieve preparation techniques requiring multiple repeated growth cycles to form a dense shell. However, this synthesis system not only necessitates the addition of ZSM-5 nuclei but also requires weak alkali treatment of the nuclei. Patent CN109569701A reports the preparation of ZSM-5 / Silicalite1 core / shell molecular sieves with high Silicalite 1 shell coverage without the addition of a template agent. The synthesis system incorporates ZSM-5 nuclei and alkali metal ions (requiring ammonium exchange).In summary, there are currently no patents or literature reports on the regulation of acid distribution in ZSM-5@Silicalite-1 core-shell materials, while the acid distribution of core-shell materials is directly related to the stability and shape selectivity of catalysts. Summary of the Invention
[0005] This application relates to a method for modulating the acid site distribution of ZSM-5@Silicalite-1 core-shell material, mainly addressing the technical problem of poor controllability of acid site distribution in existing core-shell materials. This application employs a novel seed-guided silicon source slow-release synthesis strategy. Under the premise of a fixed two-step silicon source feeding ratio, precise modulation of the acid site distribution of the core-shell material is achieved by simultaneously adjusting the content and size of the Silicalite-1 seed crystals.
[0006] According to one aspect of this application, a method for preparing ZSM-5@Silicalite-1 core-shell molecular sieve is provided, comprising the following steps:
[0007] Aluminum source, silicon source I, template agent, Silicalite-1 seed crystal, water and alkali are mixed and crystallized into I. Then silicon source II and water are added and crystallized into II in a sealed container. After drying, the ZSM-5@Silicalite-1 core-shell molecular sieve is obtained.
[0008] Silicalite-1 is the core, and ZSM-5 is the shell.
[0009] The size of the Silicalite-1 seed crystal is 20 nm to 5.0 μm.
[0010] The aluminum source is selected from at least one of sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum isopropoxide.
[0011] The silicon source I is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, silica gel, fumed silica, and activated clay.
[0012] The template agent is selected from at least one of tetrapropylammonium bromide, tetrapropylammonium chloride, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrabutylammonium bromide, and tetrabutylammonium chloride;
[0013] The alkali is selected from at least one of ammonia, ethylamine, n-butylamine, cyclohexylamine, ethylenediamine, diethylamine, triethylamine, sodium hydroxide, ammonia, sodium aluminate, potassium hydroxide, and sodium carbonate.
[0014] The silicon source II is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, silica gel, fumed silica, and activated clay.
[0015] The ratio of the molar amount of aluminum in the aluminum source to the total molar amount of silicon in silicon source I and silicon source II is 0.001 to 0.05.
[0016] The molar amount of the template agent is in the ratio of the total molar amount of silicon in silicon source I and silicon source II to 0.02 to 0.4.
[0017] The ratio of the molar amount of water to the total molar amount of silicon in silicon source I and silicon source II is 5 to 240.
[0018] The molar amount of the alkali is in the ratio of the total molar amount of silicon in silicon source I and silicon source II to 0.02 to 0.40.
[0019] The molar ratio of silicon element in silicon source I to the molar ratio of silicon element in silicon source II is 0.1 to 15.
[0020] The mass of silicon dioxide in the Silicalite-1 seed crystal is 0.0001 to 50 wt% of the total mass of silicon dioxide in silicon source I and silicon source II.
[0021] The temperature for crystallization I is 100–200°C;
[0022] The crystallization time is 2 to 96 hours.
[0023] The temperature for crystallization II is 100–200°C;
[0024] The crystallization time for the second stage is 2 to 96 hours.
[0025] By keeping the mass ratio of silicon source I to silicon source II constant, and simultaneously changing the size and amount of Silicalite-1 seed crystals, ZSM-5@Silicalite-1 core-shell materials with the same crystal size were obtained.
[0026] According to another aspect of this application, a ZSM-5@Silicalite-1 core-shell molecular sieve prepared by the above-described preparation method is provided.
[0027] According to another aspect of this application, an application of the above-described ZSM-5@Silicalite-1 core-shell molecular sieve is provided for the reaction of aromatic compounds with low-carbon compounds;
[0028] The aromatic compound is selected from at least one of toluene, ethylbenzene, propylbenzene, butylbenzene, naphthalene, methylnaphthalene, and biphenyl;
[0029] The low-carbon compound is selected from at least one of methanol, ethanol, propanol, butanol, ethylene, and propylene.
[0030] The beneficial effects that this application can produce include:
[0031] This application solves the problem of the untunable acid site distribution of ZSM-5@Silialite-1 core-shell material. The method provided in this application has the characteristics of simple operation, cheap and readily available raw materials, high single-reactor yield and good reproducibility, and is easy to scale up for industrial synthesis. Attached Figure Description
[0032] Figure 1 The image shown is a scanning electron microscope (SEM) image of the seed crystal in Example 1, with a scale of ~150 nm.
[0033] Figure 2 The image shown is a scanning electron microscope (SEM) image of the core-shell material sample prepared in Example 1, with a scale of ~6 μm.
[0034] Figure 3 The image shown is a scanning electron microscope (SEM) image of the seed crystal in Example 2, with a scale of ~300 nm.
[0035] Figure 4 The image shown is a scanning electron microscope (SEM) image of the core-shell material sample prepared in Example 2, with a scale of ~6 μm.
[0036] Figure 5 The image shown is a scanning electron microscope (SEM) image of the seed crystal in Example 3, with a scale of ~450 nm.
[0037] Figure 6 The image shown is a scanning electron microscope (SEM) image of the core-shell material sample prepared in Example 3, with a scale of ~6 μm.
[0038] Figure 7 The image shown is a scanning electron microscope (SEM) image of the seed crystal in Example 4, with a scale of ~600 nm.
[0039] Figure 8 The image shown is a scanning electron microscope (SEM) image of the core-shell material sample prepared in Example 4, with a scale of ~6 μm.
[0040] Figure 9 This is a schematic diagram of the structure of the ZSM-5@Silicalite-1 core-shell material prepared in this application. Detailed Implementation
[0041] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.
[0042] Unless otherwise specified, all raw materials and reagents used in the embodiments of this application were purchased commercially.
[0043] The analysis method in the embodiments of this application is as follows:
[0044] SEM morphology analysis was performed using an S-5500 scanning electron microscope.
[0045] Example 1:
[0046] The raw materials used are as follows:
[0047] A. Silica
[0048] B. Aluminum chloride hexahydrate
[0049] C. Ethylamine aqueous solution
[0050] D. Tetrapropylammonium bromide (TPABr)
[0051] The molar composition of the raw material mixture was: SiO2 / Al2O3 = 320, ethylamine / SiO2 = 0.12, TPABr / SiO2 = 0.04, H2O / SiO2 = 25. Under stirring conditions, 60 wt% silica, aluminum chloride, ethylamine aqueous solution, deionized water, TPABr, and 0.008%–150 nm Silicalite-1 seed crystals were added to the reactor in a specific order. After stirring evenly, the mixture was placed in a crystallization vessel and dynamically crystallized at 170℃ for 48 h. After crystallization, the remaining 40 wt% silica was added, and crystallization continued at 170℃ for 24 h. Then, the mixture was cooled to room temperature, washed with deionized water until neutral, and dried overnight at 120℃ to obtain the molecular sieve powder. The solid yield reached over 95%. Figure 1 A scanning electron microscope image of a ~150nm Silicalite-1 seed crystal. Figure 2 The image shows a scanning electron microscope (SEM) image of the obtained ZSM-5@Silicalite-1 core-shell material, which has a regular morphology and uniform size (~6.0 μm).
[0052] Figure 9 This is a schematic diagram of the ZSM-5@Silicalite-1 core-shell material prepared in this application. Due to the influence of the inert shell (excluding aluminum sites), the aluminum distribution of different core-shell materials can be modulated by varying the Silicalite-1 seed size.
[0053] Example 2:
[0054] The raw materials used are as follows:
[0055] A. Silica
[0056] B. Aluminum chloride hexahydrate
[0057] C. Ethylamine aqueous solution
[0058] D. Tetrapropylammonium hydroxide (TPAOH)
[0059] The molar composition of the raw material mixture was: SiO2 / Al2O3 = 320, ethylamine / SiO2 = 0.12, TPAOH / SiO2 = 0.04, and H2O / SiO2 = 25. Under stirring conditions, 60 wt% silica, aluminum chloride, ethylamine aqueous solution, deionized water, TPAOH, and 0.05%–300 nm Silicalite-1 seed crystals were added to the reactor in a specific order. After stirring evenly, the mixture was placed in a crystallization vessel and dynamically crystallized at 170℃ for 48 h. After crystallization, the remaining 40 wt% silica was added, and crystallization continued at 170℃ for 24 h. Then, the mixture was cooled to room temperature, washed with deionized water until neutral, and dried overnight at 120℃ to obtain the molecular sieve powder. The solid yield reached over 95%. Figure 3 A scanning electron microscope image of a ~300nm Silicalite-1 seed crystal. Figure 4 The image shows a scanning electron microscope (SEM) image of the obtained ZSM-5@Silicalite-1 core-shell material, which has a regular morphology and uniform size (~6.0 μm).
[0060] Example 3:
[0061] The raw materials used are as follows:
[0062] A. Silica
[0063] B. Aluminum chloride hexahydrate
[0064] C. Ethylamine aqueous solution
[0065] D. Tetrapropylammonium bromide (TPABr)
[0066] The molar composition of the raw material mixture was: SiO2 / Al2O3 = 320, ethylamine / SiO2 = 0.12, TPABr / SiO2 = 0.04, and H2O / SiO2 = 25. Under stirring conditions, 60 wt% silica, aluminum chloride, ethylamine aqueous solution, deionized water, TPABr, and 0.3%–450 nm Silicalite-1 seed crystals were added to the reactor in a specific order. After stirring evenly, the mixture was placed in a crystallization reactor and dynamically crystallized at 170℃ for 48 h. After crystallization, the remaining 40 wt% silica was added, and crystallization continued at 170℃ for 24 h. Then, the mixture was cooled to room temperature, washed with deionized water until neutral, and dried overnight at 120℃ to obtain the molecular sieve powder. The solid yield reached over 95%. Figure 5 A scanning electron microscope image of a ~450nm Silicalite-1 seed crystal. Figure 6 The image shows a scanning electron microscope (SEM) image of the obtained ZSM-5@Silicalite-1 core-shell material, which has a regular morphology and uniform size (~6.0 μm).
[0067] Example 4:
[0068] The raw materials used are as follows:
[0069] A. Silica
[0070] B. Aluminum chloride hexahydrate
[0071] C. Ethylamine aqueous solution
[0072] D. Tetrapropylammonium bromide (TPABr)
[0073] The molar composition of the raw material mixture was: SiO2 / Al2O3 = 320, ethylamine / SiO2 = 0.12, TPABr / SiO2 = 0.04, and H2O / SiO2 = 25. Under stirring conditions, 60 wt% silica, aluminum chloride, ethylamine aqueous solution, deionized water, TPABr, and 2.0%–650 nm Silicalite-1 seed crystals were added to the reactor in a specific order. After stirring evenly, the mixture was placed in a crystallization reactor and dynamically crystallized at 170℃ for 48 h. After crystallization, the remaining 40 wt% silica was added, and crystallization continued at 170℃ for 24 h. Then, the mixture was cooled to room temperature, washed with deionized water until neutral, and dried overnight at 120℃ to obtain the molecular sieve powder. The solid yield reached over 95%. Figure 7 A scanning electron microscope image of a ~650nm Silicalite-1 seed crystal. Figure 8 The image shows a scanning electron microscope (SEM) image of the obtained ZSM-5@Silicalite-1 core-shell material, which has a regular morphology and uniform size (~6.0 μm).
[0074] Example 5:
[0075] The raw materials used are as follows:
[0076] A. Silica
[0077] B. Aluminum chloride hexahydrate
[0078] C. Ethylamine aqueous solution
[0079] D. Tetrapropylammonium bromide (TPABr)
[0080] The molar composition of the raw material mixture is: SiO2 / Al2O3 = 320, ethylamine / SiO2 = 0.12, TPABr / SiO2 = 0.04, H2O / SiO2 = 25. Under stirring conditions, 60wt% silica, aluminum chloride, ethylamine aqueous solution, deionized water, TPABr, and 5%–800nm Silicalite-1 seed crystals were added to the reactor in a specific order. After stirring evenly, the mixture was placed in a crystallization reactor and dynamically crystallized at 170℃ for 48h. After crystallization, the remaining 40wt% silica was added, and crystallization was continued at 170℃ for 24h. Then, the mixture was cooled to room temperature, washed with deionized water until neutral, and dried overnight at 120℃ to obtain the molecular sieve powder.
[0081] Example 6:
[0082] The raw materials used are as follows:
[0083] A. Silica
[0084] B. Aluminum chloride hexahydrate
[0085] C. Ethylamine aqueous solution
[0086] D. Tetrapropylammonium hydroxide (TPAOH, 25%)
[0087] The molar composition of the raw material mixture is: SiO2 / Al2O3 = 320, ethylamine / SiO2 = 0.12, TPAOH / SiO2 = 0.04, H2O / SiO2 = 25. Under stirring conditions, 60wt% silica, aluminum chloride, ethylamine aqueous solution, deionized water, TPAOH, and 2.0%–650nm Silicalite-1 seed crystals were added to the reactor in a specific order. After stirring evenly, the mixture was placed in a crystallization reactor and dynamically crystallized at 170℃ for 48h. After crystallization, the remaining 40wt% silica was added, and crystallization continued at 170℃ for 24h. Then, the mixture was cooled to room temperature, washed with deionized water until neutral, and dried overnight at 120℃ to obtain the molecular sieve powder.
[0088] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.
Claims
1. A method for preparing ZSM-5@Silicalite-1 core-shell molecular sieve, characterized in that, Includes the following steps: Aluminum source, silicon source I, template agent, Silicalite-1 seed crystal, water and alkali are mixed and crystallized into I. Then silicon source II and water are added and crystallized into II in a sealed container. After drying, the ZSM-5@Silicalite-1 core-shell molecular sieve is obtained. Silicalite-1 is the core, and ZSM-5 is the shell.
2. The preparation method according to claim 1, characterized in that, The size of the Silicalite-1 seed crystal is 20 nm to 5.0 μm.
3. The preparation method according to claim 1, characterized in that, The aluminum source is selected from at least one of sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum isopropoxide. The silicon source I is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, silica gel, fumed silica, and activated clay. The template agent is selected from at least one of tetrapropylammonium bromide, tetrapropylammonium chloride, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrabutylammonium bromide, and tetrabutylammonium chloride; The alkali is selected from at least one of ammonia, ethylamine, n-butylamine, cyclohexylamine, ethylenediamine, diethylamine, triethylamine, sodium hydroxide, ammonia, sodium aluminate, potassium hydroxide, and sodium carbonate. The silicon source II is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, silica gel, fumed silica, and activated clay.
4. The preparation method according to claim 1, characterized in that, The ratio of the molar amount of aluminum in the aluminum source to the total molar amount of silicon in silicon source I and silicon source II is 0.001 to 0.
05. The molar amount of the template agent is in the ratio of the total molar amount of silicon in silicon source I and silicon source II to 0.02 to 0.
4. The ratio of the molar amount of water to the total molar amount of silicon in silicon source I and silicon source II is 5 to 240. The molar amount of the alkali is in the ratio of the total molar amount of silicon in silicon source I and silicon source II to 0.02 to 0.
40. The molar ratio of silicon element in silicon source I to the molar ratio of silicon element in silicon source II is 0.1 to 15. The mass of silicon dioxide in the Silicalite-1 seed crystal is 0.0001 to 50 wt% of the total mass of silicon dioxide in silicon source I and silicon source II.
5. The preparation method according to claim 1, characterized in that, The temperature for crystallization I is 100–200°C; The crystallization time is 2 to 96 hours.
6. The preparation method according to claim 1, characterized in that, The temperature for crystallization II is 100–200°C; The crystallization time for the second stage is 2 to 96 hours.
7. A ZSM-5@Silicalite-1 core-shell molecular sieve prepared by the preparation method according to any one of claims 1 to 6.
8. An application of the ZSM-5@Silicalite-1 core-shell molecular sieve according to claim 7, characterized in that, Used for the reaction of aromatic compounds with low-carbon compounds; The aromatic compound is selected from at least one of toluene, ethylbenzene, propylbenzene, butylbenzene, naphthalene, methylnaphthalene, and biphenyl; The low-carbon compound is selected from at least one of methanol, ethanol, propanol, butanol, ethylene, and propylene.