Preparation method and application of Ni-EMT zeolite molecular sieve

Abstract

The invention belongs to the technical field of zeolite molecular sieve preparation, and particularly discloses a preparation method and application of a Ni-EMT zeolite molecular sieve.The Ni-EMT zeolite molecular sieve is prepared by using a complex of nickel nitrate hexahydrate and ethylenediamine as a nickel source and a template agent and using relatively cheap tetrabutyl ammonium hydroxide and tetraethylammonium hydroxide as synergistic template agents. According to the present invention, the Ni-EMT zeolite molecular sieve is directly prepared by using the one-pot method, the prepared Ni-EMT zeolite molecular sieve has characteristics of high crystallinity, stable molecular sieve structure, large specific surface area and large pore, and compared with the traditional method, the use of the expensive and high-toxicity 18-crown ether-6 template agent is avoided, and the metal nickel is coated in the EMT molecular sieve in situ so as to achieve the purpose of the in-situ preparation of the Ni-EMT zeolite molecular sieve. According to the present invention, the nickel loading amount of the Ni-EMT zeolite molecular sieve prepared by the method can be adjusted, such that the Ni-EMT zeolite molecular sieve can be used for the catalytic reactions such as the preparation of cyclohexylbenzene through the hydroalkylation of benzene, and can be widely used in the actual industrial application.

Description

Technical Field

[0001] This invention belongs to the field of zeolite molecular sieve preparation technology, and relates to the preparation of EMT-type zeolite molecular sieves, particularly a method for preparing Ni-EMT zeolite molecular sieves and their applications. Background Technology

[0002] In 1990, Delprato et al. successfully synthesized the pure hexagonal octahedral zeolite EMC-2, later known as EMT zeolite, using 18-crown ether-6 as a template agent. EMT zeolite belongs to the hexagonal crystal system and possesses a three-dimensional 12-membered ring channel system. Its framework includes both hypercage and hyperpocage types of supercages, which are linearly interconnected to form one-dimensional channels. The unique through-pore size facilitates the alkylation reactions of various organic compounds, such as the hydrogenation of benzene and the alkylation of isobutane / 2-butene. Therefore, EMT zeolite has attracted widespread research interest since the 20th century.

[0003] In 1995, Karim et al. successfully synthesized EMT molecular sieves with smaller and more uniform zeolite crystals by changing the amount of crown ether and adding fluoride to the synthesis system. CN1251823A (application date 2000.05.03) added a small amount of inexpensive surfactant to the EMT molecular sieve synthesis system, reducing the use of 18-crown ether-6 template agent. CN100431959C (application date 2008.11.12) used polyethylene glycol instead of 18-crown ether-6 as template agent to synthesize EMT zeolite using a conventional hydrothermal method, significantly reducing the synthesis cost. CN119490197A (application date 2025.02.21) disclosed a high-silica EMT molecular sieve with quaternary phosphorus compounds as the core template agent, solving the problems of highly toxic and expensive template agents and low silicon-to-aluminum ratio in traditional EMT molecular sieve synthesis. However, the operation steps of this patent are relatively complex, and there is still room for improvement in terms of ease of operation and industrialization efficiency. More importantly, most existing synthetic routes for EMT molecular sieves focus on reducing the use of expensive and toxic template agents. However, in catalytic reactions requiring metal active sites, the synthesized EMT molecular sieves all need to undergo post-processing steps to load metals. This complex post-processing increases energy consumption and generates large amounts of waste liquid, further limiting the practical application of EMT molecular sieves. Therefore, simultaneously addressing the issues of expensive and highly toxic template agents, in-situ metal loading, and complex synthetic steps is crucial for the development and application of EMT zeolites, but it remains extremely challenging. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing Ni-EMT zeolite molecular sieves. This invention utilizes a nickel-amine complex formed from a nickel salt and ethylenediamine as both the nickel source and template agent, supplemented by inexpensive tetrabutylammonium hydroxide and tetraethylammonium hydroxide as synergistic template agents. A one-pot method is employed to directly synthesize nickel-loaded Ni-EMT zeolite molecular sieves. This invention eliminates the need for expensive and highly toxic 18-crown ether-6 as a template agent, simplifying the operation. Furthermore, the in-situ coating of metallic nickel within the EMT zeolite framework avoids complex post-loading metal processes, reducing the preparation steps, lowering energy consumption, and minimizing wastewater production. The prepared Ni-EMT zeolite molecular sieve exhibits a stable structure, adjustable nickel loading, and demonstrates excellent catalytic performance in the hydrogenation alkylation of benzene to cyclohexylbenzene.

[0005] This invention is achieved through the following technical solution: A method for preparing Ni-EMT zeolite molecular sieves includes the following steps: S1: Dissolve the nickel source in deionized water to form a homogeneous solution; while stirring, slowly add ethylenediamine dropwise to the homogeneous solution, and continue stirring for a certain period of time after the addition to prepare a nickel-amine complex solution; S2: Mix tetrabutylammonium hydroxide solution, aluminum source, silicon source, sodium hydroxide, and high-silicon Y-nucleation seed solution in deionized water, and heat and stir for a certain time to form a homogeneous mixed solution; S3: Mix the nickel-amine complex solution prepared in step S1 with the mixed solution prepared in step S2 and heat and stir for a certain time to form a homogeneous mixed solution. S4: Place the mixed solution obtained in step S3 into a hydrothermal reactor, crystallize for a certain period of time, and then wash, dry and calcine to obtain Ni-EMT zeolite molecular sieve.

[0006] A further improvement to the present invention is as follows: The high-silicon Y-nucleus seed solution is prepared by the following steps: mixing tetraethyl orthosilicate, aluminum isopropoxide, tetraethylammonium hydroxide solution and sodium hydroxide, stirring for a certain time to form a homogeneous mixed solution; placing the mixed solution in a hydrothermal reactor for a certain time to crystallize, and then obtaining the high-silicon Y-nucleus seed solution.

[0007] In the preparation process of the above-mentioned high-silicon Y-nucleus seed solution, the mass concentration of the tetraethylammonium hydroxide solution is 20-50%, and the molar composition of the mixed solution is 1 SiO2:0.1 Al2O3:0.01 Na2O:1.2 (TEA)OH:18.3 H2O.

[0008] Preferably, the mass concentration of the tetraethylammonium hydroxide solution is 35 wt%. The stirring time is 1-3 hours, the crystallization temperature is 50-100℃, and the time is 12-24 hours.

[0009] Furthermore, in S1, the nickel source is nickel nitrate hexahydrate, and the molar ratio of the nickel source to ethylenediamine is 1:0.8~1.2.

[0010] Furthermore, in S2, the silicon source is tetraethyl orthosilicate or 30wt%~40wt% silica sol or a mixture of both; Preferably, the silicon source is 40 wt% silica sol; And / or, the aluminum source is sodium aluminate; And / or, the mass concentration of the tetrabutylammonium hydroxide solution is 20wt%~40wt%; Preferably, the mass concentration of the tetrabutylammonium hydroxide solution is 40 wt%. And / or, prepare the amount of tetrabutylammonium hydroxide solution, aluminum source, silicon source, sodium hydroxide and deionized water according to the gel molar chemical composition 1 SiO2:0.036 Al2O3:0.2 Na2O:0.2 (TBA)2O:26 H2O; And / or, the amount of the high-silicon Y-nucleation seed solution is 45% to 55% of the silica sol mass; And / or, the heating and stirring temperature is 30~50℃, and the time is 4~8h.

[0011] Furthermore, in S3, the molar ratio of the nickel-ethylenediamine complex prepared in step S1 to the silicon source in the mixed solution prepared in step S2 is 1:4~6. And / or, the heating and stirring temperature is 30~50℃, and the time is 1~3h.

[0012] Furthermore, the crystallization temperature described in S4 is 80~180℃, and the time is 1.5 days~6.5 days; Preferably, the crystallization temperature is 120°C and the time is 4.5 days; And / or, the calcination temperature is 500~600℃ and the time is 5~8h.

[0013] Preferably, the roasting temperature is 550°C and the time is 6 hours.

[0014] A further improvement of the present invention is as follows: This invention also protects the application of the Ni-EMT zeolite molecular sieve prepared by the above method in the catalytic hydrogenation alkylation reaction of benzene.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention proposes a one-pot method for synthesizing Ni-EMT zeolite molecular sieves, in which metallic nickel is introduced in situ into the zeolite molecular sieve in the form of a complex. The prepared molecular sieve can be used after only one calcination, which effectively simplifies the preparation process and solves the problems of highly toxic and expensive template agents, complex preparation process, and increased energy consumption due to post-loading of metal in existing preparation methods.

[0016] 2. The Ni-EMT zeolite molecular sieve of this invention has good crystallinity, good hydrothermal stability, large specific surface area, and abundant porosity. It can be applied to catalytic reactions such as the hydrogenation alkylation of benzene to produce cyclohexylbenzene, and has important significance in the field of practical chemical production. Attached Figure Description

[0017] Figure 1 The XRD patterns of the Ni-EMT zeolite molecular sieves synthesized in Examples 1-5 are shown below. Figure 2 The image shows a scanning electron microscope (SEM) image of the Ni-EMT-3 zeolite molecular sieve synthesized in Example 1. Figure 3 The N2 adsorption-desorption spectra of the synthesized Ni-EMT-3 zeolite molecular sieve are shown below; Figure 4 The X-ray diffraction patterns of Comparative Example 1 and Ni-EMT-3 are shown below. Figure 5 The X-ray diffraction patterns of Comparative Example 2 and Ni-EMT-3 are shown below. Figure 6 The catalytic performance of the synthesized Ni-EMT zeolite molecular sieve for the hydrogenation alkylation of benzene to cyclohexylbenzene was evaluated. Detailed Implementation

[0018] The present invention will now be described in detail with reference to specific embodiments.

[0019] Example 1

[0020] This embodiment synthesizes Ni-EMT zeolite molecular sieves using a one-pot method. The specific steps are as follows: Preparation of high-silicon Y-nucleus seed solution: Mix 10.42 g tetraethyl orthosilicate, 2.04 g aluminum isopropoxide, 25.24 g tetraethylammonium hydroxide solution (35 wt%), and 0.4 g sodium hydroxide, and stir for 2 h to form a homogeneous solution; place the solution in a hydrothermal reactor and crystallize at 60 °C for 16 h to obtain the high-silicon Y-nucleus seed solution. Preparation of nickel-ethylenediamine (Ni-EDA) complex solution: Add 0.3 g of nickel nitrate hexahydrate to 4.4 g of deionized water and stir thoroughly to dissolve. Then slowly add 1.137 g of anhydrous ethylenediamine to the above solution and continue stirring for 0.3 h.

[0021] Weigh 3.276 g of tetrabutylammonium hydroxide (40 wt%) into a beaker, then add 0.4 g of sodium hydroxide, 3.8 g of silica sol (40 wt%), 0.15 g of sodium aluminate, 1.89 g of high-silicon Y-nucleation seed solution, and 1.88 g of water. Place the mixture in a 40°C oil bath and heat with stirring. Add the previously prepared Ni-EDA solution and continue heating and vigorous stirring for 2 hours. Then, place the solution in a hydrothermal reactor and heat to 120°C for crystallization for 4.5 days. After crystallization, wash the obtained solid until neutral, dry it, and calcine it at 550°C for 6 hours to obtain Ni-EMT with a nickel content of 3%, denoted as Ni-EMT-3.

[0022] Example 2

[0023] In this embodiment, the amount of nickel nitrate hexahydrate added is 0.4266g, the amount of anhydrous ethylenediamine added is 1.6275g, and the other operations are the same as in Example 1, which will not be repeated here. Ni-EMT with a nickel content of 4% is prepared and is denoted as Ni-EMT-4.

[0024] Example 3

[0025] In this embodiment, the amount of nickel nitrate hexahydrate added is 0.5460g, the amount of anhydrous ethylenediamine added is 2.0376g, and the other operations are the same as in Example 1, which will not be repeated here. Ni-EMT with a nickel content of 5% is prepared and is denoted as Ni-EMT-5.

[0026] Example 4

[0027] In this embodiment, the amount of nickel nitrate hexahydrate added is 0.6432 g, the amount of anhydrous ethylenediamine added is 2.4651 g, and the other operations are the same as in Example 1, which will not be repeated here. Ni-EMT with a nickel content of 6% is prepared and is denoted as Ni-EMT-6.

[0028] Example 5

[0029] In this embodiment, the amount of nickel nitrate hexahydrate added is 0.812 g, the amount of anhydrous ethylenediamine added is 3.61 g, and the other operations are the same as in Example 1, which will not be repeated here. Ni-EMT with a nickel content of 10% is prepared and is denoted as Ni-EMT-10.

[0030] Comparative Example 1 To investigate the role of the nickel-amine complex in the synthetic system, ethylenediamine was used instead of the nickel-amine complex as a template agent. The preparation process is as follows: 1.137 g of anhydrous ethylenediamine was added dropwise to 4.4 g of deionized water, and the mixture was stirred continuously for 0.3 h. 3.276 g of tetrabutylammonium hydroxide was weighed and placed in a beaker, followed by the addition of 0.4 g of sodium hydroxide, 3.8 g of silica sol (40 wt%), 0.15 g of sodium aluminate, 1.89 g of high-silicon Y-nucleation seed crystals, and 1.88 g of water. The mixture was heated and stirred in a 40 °C oil bath, and the previously prepared Ni-EDA solution was added. After heating and vigorous stirring for 2 h, the solution was placed in a hydrothermal reactor and heated to 120 °C for crystallization for 4.5 days. After crystallization, the obtained solid was washed until neutral, dried, and calcined at 550 °C for 6 h to obtain the nickel-free synthetic zeolite, denoted as FAU.

[0031] Comparative Example 2 In this comparative example, pentaethylenehexamine was used instead of ethylenediamine to prepare the nickel-amine complex. Other operations were largely the same as in Example 1, and will not be repeated here. The obtained sample was denoted as Ni-AEPA.

[0032] Test case The crystal structure and crystallinity of the zeolites prepared in Examples 1-5 were evaluated using X-ray powder diffraction. The XRD results are as follows: Figure 1 and Figure 4 As shown, from Figure 1 As can be seen from the data, Examples 1-5 are all Ni-EMT zeolite molecular sieves with good crystallinity. Scanning electron microscopy and N2 adsorption-desorption analysis were performed on Example 1, and the results are as follows: Figure 2 and Figure 3 As shown, the Ni-EMT zeolite molecular sieve synthesized in this invention has a plate-like structure, uniform particle size, and a large specific surface area and pore structure, which can provide sufficient active sites and space for catalytic reactions.

[0033] The crystal structure of the zeolite prepared in Comparative Example 1 was evaluated by X-ray powder diffraction, and its XRD diffraction peaks were compared with those of Ni-EMT-3 synthesized using a nickel-ethylenediamine complex as a template. The results are as follows: Figure 4 As shown in the figure, the XRD diffraction peak pattern of Comparative Example 1 is clearly different from that of Ni-EMT-3. No characteristic diffraction peaks related to EMT zeolite appear, and all diffraction peaks highly match the characteristic peaks of the FAU configuration, indicating that the molecular sieve synthesized in Comparative Example 1 using ethylenediamine as a template is of the FAU type. This result shows that nickel in the nickel-ethylenediamine complex not only serves as a nickel source, but the nickel-ethylenediamine complex also acts as a template agent for the synthesis of Ni-EMT zeolite molecular sieves, playing a crucial guiding role in the one-pot synthesis of Ni-EMT zeolite molecular sieves.

[0034] The crystal structure of the zeolite prepared in Comparative Example 2 was evaluated by X-ray powder diffraction, and its XRD diffraction peaks were compared with those of Ni-EMT-3 synthesized using a nickel-ethylenediamine complex as a template. The results are as follows: Figure 5 As shown in the figure, it can be clearly observed that the XRD diffraction peak pattern of Comparative Example 2 does not show any characteristic diffraction peaks belonging to zeolite molecular sieves. This indicates that Ni-EMT molecular sieves cannot be synthesized by using nickel-pentaethylenehexamine instead of nickel-ethylenediamine complex as a template. This further proves that the nickel-ethylenediamine complex has a unique guiding role in the one-pot synthesis of Ni-EMT zeolite molecular sieves.

[0035] Application examples To verify the catalytic performance of the Ni-EMT zeolite molecular sieve prepared in this invention, the Ni-EMT molecular sieve catalysts prepared in Examples 1, 4, and 5 were calcined at 500°C for 5 hours in a tube furnace under an H2 / Ar atmosphere for reduction treatment. A benzene hydrogenation alkylation reaction system was constructed using a 100 mL stainless steel micro-high-pressure reactor. Under conditions of 200°C and 4 MPa H2 pressure, 10 g of benzene (purity ≥99.9%), 2 g of n-decane (purity ≥99.5%), and 0.4 g of Ni-EMT zeolite catalyst were added to the 100 mL stainless steel micro-reactor, and the reaction was carried out at 200°C and 800 rpm for 3 hours with stirring to study the hydrogenation alkylation performance of benzene. The results are as follows: Figure 6 As shown, under these reaction conditions, all three catalysts exhibited certain benzene hydrogenation alkylation activity, with the Ni-EMT-10 sample showing the best activity, achieving a benzene conversion of 56% and a cyclohexylbenzene selectivity of 21%, demonstrating good potential for benzene hydrogenation alkylation applications.

[0036] The above description of the embodiments is only for illustrating the technical concept and features of the present invention. Its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. Those skilled in the art can obviously easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the above embodiments should not be used to limit the scope of protection of the present invention. All improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A process for the preparation of a Ni-EMT zeolite molecular sieve, characterized by, The method comprises the following steps: S1: dissolving a nickel source in deionized water to form a uniform solution; slowly adding ethylenediamine to the uniform solution while stirring; and continuing to stir for a certain period of time to prepare a nickel-amine complex solution; S2: mixing a tetrabutylammonium hydroxide solution, an aluminum source, a silicon source, sodium hydroxide and a high-silicon Y nucleus seed solution in deionized water, and heating and stirring for a certain period of time to form a uniform mixed solution; S3: mixing the nickel-amine complex solution prepared in S1 with the mixed solution prepared in S2, and heating and stirring for a certain period of time to form a uniform mixed solution; S4: placing the mixed solution obtained in S3 into an autoclave, crystallizing for a certain period of time, and then washing with water, drying and calcining to obtain the Ni-EMT zeolite molecular sieve.

2. The method for preparing a Ni-EMT zeolite molecular sieve according to claim 1, characterized by: The high-silicon Y nucleus seed solution is prepared by the following steps: mixing tetraethyl orthosilicate, aluminum isopropoxide, a tetrabutylammonium hydroxide solution and sodium hydroxide, and stirring for a certain period of time to form a uniform mixed solution; and placing the mixed solution in an autoclave and crystallizing for a certain period of time to obtain the high-silicon Y nucleus seed solution.

3. The method for preparing a Ni-EMT zeolite molecular sieve according to claim 2, characterized by: The mass concentration of the tetrabutylammonium hydroxide solution is 20-50%, and the molar composition of the mixed solution is 1 SiO2:0.1 Al2O3:0.01Na2O:1.2 (TEA)OH:18.3 H2O.

4. The method for preparing a Ni-EMT zeolite molecular sieve according to claim 2, characterized by: The stirring time is 1-3h, and the crystallization temperature is 50-100℃ and the time is 12h-24h.

5. The method for preparing a Ni-EMT zeolite molecular sieve according to claim 1, characterized by: In S1, the nickel source is nickel nitrate hexahydrate, and the molar ratio of the nickel source to ethylenediamine is 1:0.8-1.

2.

6. The method for preparing a Ni-EMT zeolite molecular sieve according to claim 1, characterized by: In S2, the silicon source is tetraethyl orthosilicate or a 30wt%-40wt% silica sol or a mixture of the two; and / or, the aluminum source is sodium aluminate; and / or, the mass concentration of the tetrabutylammonium hydroxide solution is 20wt%-40wt%; and / or, the amounts of the tetrabutylammonium hydroxide solution, the aluminum source, the silicon source, sodium hydroxide and deionized water are configured according to the molar chemical composition of the gel 1 SiO2:0.036 Al2O3:0.2 Na2O:0.2 (TBA)2O:26 H2O; and / or, the amount of the high-silicon Y nucleus seed solution is 45%-55% of the mass of the silica sol; and / or, the heating and stirring temperature is 30-50℃ and the time is 4-8h.

7. The method for preparing a Ni-EMT zeolite molecular sieve according to claim 1, characterized by: In S3, the molar ratio of the nickel-ethylenediamine complex prepared in S1 to the silicon source in the mixed solution prepared in S2 is 1:4-6; and / or, the heating and stirring temperature is 30-50℃ and the time is 1-3h.

8. The method for preparing a Ni-EMT zeolite molecular sieve according to claim 1, characterized by: In S4, the crystallization temperature is 80-180℃ and the time is 1.5 days-6.5 days; and / or, the calcination temperature is 500-600℃ and the time is 5-8h.

9. The application of the Ni-EMT zeolite molecular sieve prepared by the method of any one of claims 1-8 in catalyzing the hydrogenation alkylation reaction of benzene.

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