In-situ synthesis of ammonium-type zsm-5 / silicalite-1 core-shell molecular sieve, method and application thereof

Abstract

The application relates to in-situ synthesis of ammonium type ZSM-5 / Silicalite-1 core-shell molecular sieve, a method and application thereof, and mainly solves the technical problems of complex preparation process steps, ammonium exchange, and more wastewater in existing core-shell material preparation processes. A one-pot synthesis method of batch feeding of a silicon source is adopted, the complex preparation process of the core-shell material is simplified into one step, and the synthesis mother liquor does not contain alkali metal ions. The core-shell molecular sieve prepared by the method has the advantages of uniform size, adjustable silicon-aluminum ratio and adjustable core-shell ratio, in addition, the obtained ammonium type core-shell molecular sieve can be directly used for reaction evaluation after calcination, and the ammonium type core-shell molecular sieve exhibits high para-methyl ethylbenzene selectivity in a shape-selective alkylation reaction of toluene and ethylene.

Description

Technical Field

[0001] This application relates to an in-situ synthesis of ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieves, a method thereof, and its application, belonging to the field of molecular sieve synthesis. Background Technology

[0002] Para-substituted methylethylbenzene, diethylbenzene, and xylene are raw materials for the production of key polymer monomers, currently mainly obtained through aromatics extraction processes in petroleum refining. The production of para-substituted methylethylbenzene, diethylbenzene, and xylene via alkylation reactions using toluene, ethylbenzene, benzene, methanol, and ethylene as raw materials has the advantages of a wide range of reactant sources and reduced dependence on petroleum feedstocks, making it of significant research value. Alkylation is a typical acid-catalyzed process, with traditional alkylation catalysts being homogeneous acid catalysts such as AlCl3 and H2SO4, but acidic molecular sieve-based catalytic materials have gradually emerged. Among them, ZSM-5 zeolite exhibits high activity in gas-phase alkylation reactions such as toluene-ethylene, toluene-methanol, and ethylbenzene-ethylene. However, the products are usually 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, the catalyst preparation is costly and has poor reproducibility. However, coating the surface of ZSM-5 with pure silica MFI zeolite (Silicalite-1) to prepare a 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 nucleating 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 material. 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 / Silicalite 1 core / shell molecular sieves with high Silicalite 1 shell coverage without the addition of a template agent, introducing ZSM-5 nuclei and alkali metal ions (requiring ammonium exchange) into the synthesis system.In summary, previous preparations of core-shell materials all involved the addition of ZSM-5 nuclei, with high requirements for the quality of the ZSM-5 nuclei. Furthermore, most required additional ammonium exchange treatment, making the overall preparation process complex. Therefore, there is an urgent need to develop a new, controllable synthesis method for ZSM-5 / Silicalite-1 core-shell materials. Summary of the Invention

[0005] This application employs a one-pot synthesis method with batch-feeding silicon sources, simplifying the complex preparation process of core-shell materials into a single step, and the synthesis mother liquor does not contain alkali metal ions. The core-shell molecular sieves prepared by this method have advantages such as uniform size, adjustable silicon-to-aluminum ratio, and adjustable core-shell ratio. Furthermore, the obtained ammonium-type core-shell molecular sieves can be directly used for reaction evaluation after calcination.

[0006] According to one aspect of this application, a method for in-situ synthesis of ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieves is provided, comprising the following steps:

[0007] Raw materials containing aluminum source, silicon source I, template agent, water and alkali are mixed, crystallized into I, and then silicon source II is added. Crystallization II is carried out in a sealed container and dried to obtain the ammonium type ZSM-5 / Silicalite-1 core-shell molecular sieve.

[0008] The aluminum source is selected from at least one of sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum isopropoxide.

[0009] The silicon source I is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, silica gel, fumed silica, and activated clay.

[0010] The template agent is selected from at least one of n-butylamine, tetrapropylammonium bromide, tetrabutylammonium bromide, tetraethylammonium bromide, 1,6-hexanediamine, cyclohexylamine, tetrabutylammonium hydroxide, and ethylamine;

[0011] The alkali is selected from at least one of ammonia, ethylamine, n-butylamine, cyclohexylamine, ethylenediamine, diethylamine, and triethylamine;

[0012] The silicon source II is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, silica gel, fumed silica, and activated clay.

[0013] 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.

[0014] Optionally, 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 any value from 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05 or any value between the two.

[0015] 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 0.40.

[0016] Optionally, the ratio of the molar amount of the template agent to the total molar amount of silicon in silicon source I and silicon source II is any value from 0.02, 0.05, 0.10, 0.20, 0.30, 0.40 or any value between the two.

[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 120.

[0018] Optionally, the ratio of the molar amount of water to the total molar amount of silicon in silicon source I and silicon source II is any value among 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120, or any value between the two.

[0019] The ratio of the molar amount of the alkali to the total molar amount of silicon in silicon source I and silicon source II is 0.02 to 0.40.

[0020] Optionally, the ratio of the molar amount of the alkali to the total molar amount of silicon in silicon source I and silicon source II is any value from 0.02, 0.05, 0.10, 0.20, 0.30, 0.40 or a range between any two.

[0021] The molar ratio of silicon in silicon source I to silicon in silicon source II is 0.1 to 15.

[0022] Optionally, the ratio of the molar amount of silicon in silicon source I to the molar amount of silicon in silicon source II is any value among 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15, or any range between the two.

[0023] The temperature for crystallization I is 100–200°C;

[0024] Optionally, the crystallization temperature I is any value or a range between 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C.

[0025] The crystallization time for I is 2–96 hours;

[0026] Optionally, the crystallization time I is any value among 2h, 4h, 8h, 16h, 32h, 64h, and 96h, or a range between any two.

[0027] The temperature for crystallization II is 100–200°C;

[0028] Optionally, the crystallization temperature II is any value or a range between 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C.

[0029] The crystallization time for the second stage is 2 to 96 hours.

[0030] Optionally, the crystallization time I is any value among 2h, 4h, 8h, 16h, 32h, 64h, and 96h, or a range between any two.

[0031] The drying temperature is 50–200°C;

[0032] Optionally, the drying temperature is any value among 50°C, 100°C, 150°C, and 200°C, or a range between any two.

[0033] The drying time is 2 to 24 hours;

[0034] Optionally, the drying time is any value among 2h, 6h, 12h, 18h, and 24h, or a range between any two.

[0035] After crystallization II and before drying, the material undergoes washing and solid-liquid separation.

[0036] According to another aspect of this application, an ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is provided, which is prepared by the method described above.

[0037] The silicon-to-aluminum ratio of the ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is 20–1000.

[0038] Optionally, the silica-alumina ratio of the ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is any value among 20, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000, or a range between any two.

[0039] The size of the ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is 0.2–10.0 μm.

[0040] Optionally, the size of the ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is any value among 0.2μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, and 10μm, or any value between both.

[0041] According to another aspect of this application, a method for shape-selective alkylation of toluene / ethylene is provided, characterized in that...

[0042] The above-mentioned ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve was used.

[0043] The ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is formed by extrusion and calcination.

[0044] The beneficial effects that this application can produce include:

[0045] This application solves the problems of high cost, high requirements for ZSM-5 crystal quality, extremely low single-reactor yield and poor product reproducibility in the preparation of ZSM-5@S-1 core-shell materials by traditional synthesis methods, which limit its large-scale industrial production. 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

[0046] Figure 1 This is a scanning electron microscope image of the sample from Example 1.

[0047] Figure 2 The X-ray photoelectron spectrum of the sample in Example 1 is shown.

[0048] Figure 3 This is a scanning electron microscope image of the sample from Example 2.

[0049] Figure 4 This study evaluates the shape-selective alkylation performance of the toluene and ethylene samples in Example 1.

[0050] Figure 5 This is an evaluation of the shape-selective alkylation performance of the toluene and ethylene samples in Example 2. Detailed Implementation

[0051] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0052] Unless otherwise specified, all raw materials and reagents used in the embodiments of this application were purchased commercially.

[0053] The analysis method in the embodiments of this application is as follows:

[0054] SEM morphology analysis was performed using an S-5500 scanning electron microscope.

[0055] X-ray photoelectron spectroscopy analysis was performed using an ESCALAB 250.

[0056] Example 1:

[0057] The raw materials used are as follows:

[0058] A. Silica

[0059] B. Aluminum chloride hexahydrate

[0060] C. Ethylamine aqueous solution

[0061] D. Tetrapropylammonium bromide (TPABr)

[0062] 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, and TPABr were added to a reaction vessel in a specific order. After thorough mixing, the mixture was placed in a crystallization vessel and dynamically crystallized at 170℃ for 48 hours. After crystallization, the remaining 40 wt% silica was added, and crystallization continued at 170℃ for another 24 hours. The mixture was then 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 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). Figure 2 The X-ray photoelectron spectroscopy of the sample showed that its surface contained almost no aluminum, with a surface SiO2 / Al2O3 ratio of 2130. The XRF results showed that its bulk SiO2 / Al2O3 ratio was 310, proving the successful preparation of the core-shell material.

[0063] Example 2:

[0064] The raw materials used are as follows:

[0065] A. Silica sol

[0066] B. Aluminum nitrate nonahydrate

[0067] C. Ammonia

[0068] D. Tetrapropylammonium bromide (TPAOH)

[0069] The molar composition of the raw material mixture is: SiO2 / Al2O3 = 250, ammonia / SiO2 = 0.08, TPAOH / SiO2 = 0.08, H2O / SiO2 = 40. Under stirring conditions, 80 wt% silica sol, aluminum nitrate, ammonia, deionized water, and TPAOH are added to the reactor in a certain order. After stirring evenly, the mixture is placed in a crystallization reactor and dynamically crystallized at 170℃ for 24 h. After crystallization, the remaining 20 wt% silica sol is added, and crystallization continues at 170℃ for 48 h. Then, the mixture is cooled to room temperature, washed with deionized water until neutral, and dried overnight at 120℃ to obtain molecular sieve powder. Figure 3 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 (~1.8 μm). X-ray photoelectron spectroscopy results show that the surface SiO2 / Al2O3 ratio is 1050, while XRF results show that the bulk SiO2 / Al2O3 ratio is 245, proving the successful preparation of the core-shell material.

[0070] Examples 3-8:

[0071] Examples 3-8 are core-shell molecular sieves synthesized according to the synthesis ratios and conditions in Table 1, following similar methods and steps as in Example 1. See Table 1 for details.

[0072]

[0073]

[0074] Example 7

[0075] The core-shell material obtained in Example 1 was extruded into strips using Al2O3 as the binder, with a binder-to-molecular-sieve ratio of 15:85. After extrusion, the strips were dried, calcined, and crushed into 20-40 mesh. Its shape-selective alkylation performance for toluene and ethylene was evaluated using a fixed-bed reactor with a catalyst loading of 3.0 g, a reaction temperature of 370 °C, and an ethylene space velocity of 0.3 h⁻¹. -1 The toluene / ethylene molar ratio was 7, and the reaction pressure was atmospheric pressure. The reaction results are as follows: Figure 4 As shown, the selectivity of p-methylethylbenzene reaches approximately 95% during the stable period.

[0076] Example 8

[0077] The core-shell material obtained in Example 2 was extruded into strips using Al2O3 as the binder, with a binder-to-molecular-sieve ratio of 15:85. After extrusion, the strips were dried, calcined, and crushed into 20-40 mesh. Its shape-selective alkylation performance for toluene and ethylene was evaluated using a fixed-bed reactor with a catalyst loading of 3.0 g, a reaction temperature of 370 °C, and an ethylene space velocity of 0.3 h⁻¹. -1 The toluene / ethylene molar ratio was 7, and the reaction pressure was 0.5 MPa. The reaction results are as follows: Figure 5 As shown, the selectivity for p-methylethylbenzene can reach over 90%.

[0078] 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 in-situ synthesis of ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieves, characterized in that, Includes the following steps: The raw materials containing aluminum source, silicon source I, template agent, water and alkali are mixed, crystallized into I, then silicon source II is added, crystallized into II in a sealed container, and dried to obtain the ammonium type ZSM-5 / Silicalite-1 core-shell molecular sieve. The alkali is selected from at least one of ammonia, ethylamine, n-butylamine, cyclohexylamine, ethylenediamine, diethylamine, and triethylamine; 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 0.02 to 0.4 times the total molar amount of silicon in silicon source I and silicon source II. 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 120. The ratio of the molar amount of the alkali to the total molar amount of silicon in silicon source I and silicon source II is 0.02 to 0.

40. The temperature of crystallization I is 100~200℃; the time of crystallization I is 2~96h; The temperature of crystallization II is 100~200℃; the time of crystallization II is 2~96h.

2. The 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 n-butylamine, tetrapropylammonium bromide, tetrabutylammonium bromide, tetraethylammonium bromide, 1,6-hexanediamine, cyclohexylamine, tetrabutylammonium hydroxide, and ethylamine; The silicon source II is selected from at least one of tetraethyl orthosilicate, silica sol, water glass, silica gel, fumed silica, and activated clay.

3. The method according to claim 1, characterized in that, The molar ratio of silicon in silicon source I to silicon in silicon source II is 0.1 to 15.

4. The method according to claim 1, characterized in that, The drying temperature is 50~200℃; The drying time is 2-24 hours; After crystallization II and before drying, the material undergoes washing and solid-liquid separation.

5. An ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve, characterized in that, It is prepared by the method described in any one of claims 1 to 4.

6. The ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve according to claim 5, characterized in that, The silicon-to-aluminum ratio of the ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is 20~1000; The size of the ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is 0.2~10.0 μm.

7. A method for shape-selective alkylation of toluene / ethylene, characterized in that, The ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve as described in any one of claims 5 or 6 is used.

8. The method according to claim 7, characterized in that, The ammonium-type ZSM-5 / Silicalite-1 core-shell molecular sieve is formed by extrusion.

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