Mww structure molecular sieve and preparation method and application thereof
By using a synergistic assisted crystallization method with seed crystals and low-toxicity organic amine templates, the problem of synthesizing MCM-22 molecular sieves was solved, and the preparation of inexpensive and green MWW-structured molecular sieves with excellent catalytic performance was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2022-11-08
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies make it difficult to synthesize MCM-22 molecular sieves without using hexamethyleneimine, piperidine, or piperazine, and traditional template agents have problems such as volatility, flammability, high toxicity, or high cost.
MWW-structured molecular sieves were synthesized using seed crystals and two low-toxicity, inexpensive organic amines as template agents via a synergistic assisted crystallization method. The first template agent was used to construct the basic layer structure, and the second template agent was used to form interlayer hydrogen bonds, avoiding the use of hexamethyleneimine, piperidine, and high-piperazine.
Without using traditional template agents, MWW-structured molecular sieves with interlayer hydrogen bonds were successfully synthesized, exhibiting catalytic activity similar to MCM-22 molecular sieves, which improved the operability and catalytic activity of production and reduced costs.
Smart Images
Figure CN118005030B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of molecular sieve material synthesis technology, and in particular to an MWW structured molecular sieve, its preparation method, and its application. Background Technology
[0002] MWW-structured molecular sieves exhibit a highly typical two-dimensional plate-like morphology. Their plate-like structure is composed of several basic monolayers stacked together, forming a unique channel structure, primarily consisting of two-dimensional sinusoidal ten-membered ring channels along the ab-axis plane and twelve-membered ring supercage and semi-supercage structures along the c-axis direction. The ten-membered ring channels have an opening size of 0.41 nm × 0.51 nm and are distributed outside the supercage structure; the twelve-membered ring supercages have a size of 0.71 nm × 0.71 nm × 1.82 nm and communicate with six identical supercages in the surrounding ab-axis plane through the ten-membered rings; the semi-supercages distributed on the plate surface have a size of 0.71 nm × 0.71 nm × 0.8 nm, and their open twelve-membered openings are highly conducive to reactant diffusion, exhibiting excellent catalytic performance for macromolecular reactions. They have been widely used in reactions such as alkylation.
[0003] MWW-structured molecular sieves can be further subdivided into several varieties based on the different stacking methods of their basic monolayers. These mainly include MCM-22 molecular sieves, MCM-49 molecular sieves with oxygen bridges between monolayers, MCM-36 molecular sieves with a pillar-like structure between layers, MCM-56 molecular sieves with disordered stacking between layers, and ITQ-2 molecular sieves with a monolayer structure. MCM-22 molecular sieves are obtained by calcining and dehydrating the interlayer silanol groups to form oxygen bridges. The crystal structure of calcined MCM-22 molecular sieves is the same as that of MCM-49 molecular sieves.
[0004] Template agents used for the direct induced synthesis of MWW-structured molecular sieves generally include hexamethyleneimine, piperidine, and homopiperazine. Hexamethyleneimine is the most widely used, but it suffers from drawbacks such as volatility, flammability, and high toxicity. Piperidine is difficult to obtain commercially. Homopiperazine is expensive and therefore difficult to apply. Therefore, developing a cost-effective and environmentally friendly method for synthesizing MWW-structured molecular sieves is crucial.
[0005] The synthesis of existing MWW-structured molecular sieves typically involves combining hexamethyleneimine with another organic amine to synthesize molecular sieves such as MCM-22.
[0006] Existing technologies reveal that due to the unique structure of MWW molecular sieves, direct synthesis using seed crystals is impossible. However, by adding organic amines to the seed crystals, a complete MCM-49 molecular sieve can be constructed. Currently, there is no precedent for synthesizing MCM-22 molecular sieves without using hexamethyleneimine, piperidine, or perpiperazine. Therefore, there is an urgent need to develop a highly operable, green, and inexpensive method for preparing MWW molecular sieves such as MCM-22. Summary of the Invention
[0007] To address the aforementioned problems, the present invention aims to provide an MWW-structured molecular sieve, its preparation method, and its applications. This invention utilizes a method of synergistic crystallization with seed crystals and two template agents to directly synthesize MWW-structured molecular sieves without using hexamethyleneimine, piperidine, or piperazine.
[0008] To achieve the above objectives, the present invention provides a method for preparing MWW-structured molecular sieves. The method includes: mixing an aluminum source, water, an alkali source, a first template agent, a second template agent, a silicon source, and seed crystals to form a gel, and then crystallizing the gel to obtain the MWW-structured molecular sieve; wherein the first template agent includes cyclohexylamine, and the second template agent may include diisopropylamine (molecular formula C6H). 15 N), di-n-butylamine (molecular formula C8H) 19 N), diisobutylamine (molecular formula C8H) 19 N), 1,4-diazabicyclo[2.2.2]octane (molecular formula C6H) 12 N2), 1,6-hexanediamine (molecular formula C6H) 16 N2), N,N,N,N-Tetramethyl-1,6-hexanediamine (CAS No. 111-18-2, molecular formula C 10 H 24 One or more combinations of N2).
[0009] In the above preparation method, both the first and second template agents are low-toxicity and inexpensive organic amines. The first template agent, as the main template agent, can work in conjunction with seed crystals to construct the basic layer structure of the molecular sieve. The second template agent, as the secondary template agent, has 6-10 carbon atoms and sp. N atoms. 3 Hybridized aliphatic amines can rely on the nitrogen atom sp 3 The empty orbital vacancies in the hybrid orbitals form interlayer hydrogen bonds with the silanol groups on the surface of the monolayer structure, and the process of forming hydrogen bonds does not affect the overall crystallization effect of the molecular sieve. Therefore, in some embodiments, the MWW-structured molecular sieve obtained by the above preparation method has interlayer hydrogen bonds formed between the silanol groups and the second template agent.
[0010] This invention has discovered that it is impossible to obtain MWW-structured molecular sieves with interlayer hydrogen bonds using only one of the first template agent, second template agent, or seed crystal. For example, omitting the second template agent, using only the first template agent and seed crystal only yields MCM-49 molecular sieve, where the interlayer bonds are oxygen bridges rather than hydrogen bonds. The preparation method provided by this invention, through the synergistic effect of the first template agent, second template agent, and seed crystal, can synthesize MWW-structured molecular sieves with interlayer hydrogen bonds without omitting hexamethyleneimine, piperidine, and perpiperazine. In some specific embodiments, the molar ratio of the first template agent to the second template agent is generally controlled at 0.5-20:1, for example, it can be controlled at 0.5-1.5:1.
[0011] In a specific embodiment of the present invention, the alkali source is denoted as MOH (M is the atom in the alkali source that forms a cation, and the valence state of M is generally monovalent, for example, if the alkali source is NaOH, then M is Na), the silicon source is SiO2, the aluminum source is Al2O3, the alkali source is M2O, the sum of the first template agent and the second template agent is denoted as T, and the chemical composition of the gel generally satisfies the following molar ratio ranges: Al2O3 / SiO2 = 0.005-0.05, M2O / SiO2 = 0.03-0.50, T / SiO2 = 0.10-0.75, H2O / SiO2 = 8-120; the seed crystal, based on dry weight, generally satisfies the following mass ratio of seed crystal to silicon source: seed crystal / SiO2 = 0.01-0.25.
[0012] In some specific embodiments, the silicon source and aluminum source can satisfy the following molar ratio: Al2O3 / SiO2 = 0.01-0.05, and more specifically, Al2O3 / SiO2 = 0.01-0.02.
[0013] In some specific implementations, the silicon source and water can satisfy the following molar ratio: H2O / SiO2 = 15-120, or H2O / SiO2 = 8-13.
[0014] In specific embodiments of the present invention, the crystallization temperature is generally controlled at 120-170℃, for example, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, etc. The crystallization time is generally controlled at 12-120h, for example, 12h, 20h, 30h, 40h, 50h, 60h, 70h, 72h, 80h, 90h, 100h, 110h, 120h, etc.
[0015] In a specific embodiment of the present invention, the silicon source may include silicon dioxide, silicates, silicate esters, etc. Specifically, the silicon source may include one or a combination of two or more of silica sol, solid silica gel, fumed silica, water glass, tetraethyl orthosilicate, etc.
[0016] In a specific embodiment of the present invention, the aluminum source may include one or more of the following: aluminates (such as sodium aluminate), aluminum sulfate, alumina, boehmite, etc.
[0017] In specific embodiments of the present invention, the seed crystals are generally molecular sieves with a MWW topology, such as commercially available MCM-22 molecular sieves or MCM-49 molecular sieves. In some specific embodiments, the seed crystals may also be molecular sieves with an MWW topology obtained by the preparation method of the present invention. Preferably, the seed crystals are untemplated MCM-22 molecular sieves, which contain interlayer hydrogen bonds. Using these seed crystals in the above preparation process is beneficial for obtaining MWW-structured molecular sieves with interlayer hydrogen bonds and a structure similar to that of MCM-22 molecular sieves.
[0018] In a specific embodiment of the present invention, the alkali source may include sodium hydroxide and / or potassium hydroxide, etc.
[0019] In a specific embodiment of the present invention, the above preparation method may include: mixing an aluminum source, water, an alkali source, a first template agent, and a second template agent to obtain an intermediate solution; adding a silicon source and seed crystals to the intermediate solution; mixing to form a gel; and crystallizing the gel to obtain the MWW-structured molecular sieve. By employing the above-described sequential synthesis, it is beneficial to uniformly disperse the raw materials and promote the crystallization reaction. In some specific embodiments, the first and second template agents are added after the aluminum source, which helps the aluminum source to completely dissolve and disperse uniformly in the solution. The silicon source can be added slowly, and the seed crystals can be added after the silicon source, which can improve the uniformity and stability of the reaction system and avoid the problem of uneven dispersion of the reaction system caused by the rapid addition of the silicon source and the formation of a colloid with the aluminum source.
[0020] This invention also provides an MWW-structured molecular sieve obtained by the above preparation method. The MWW-structured molecular sieve provided by this invention has an MWW topology and interlayer hydrogen bonds. In some specific embodiments, the XRD patterns of the above-mentioned MWW-structured molecular sieve exhibit relatively obvious characteristic peaks at approximately 6.5-7.15° (e.g., 7.09°) and 7.18°.
[0021] The MWW-structured molecular sieve of this invention possesses interlayer hydrogen bonds and has a structure similar to that of the uncalcined (and template-unremoved) MCM-22 molecular sieve, therefore it can be considered a precursor to the MCM-22 molecular sieve (which can be denoted as MCM-22(P) molecular sieve). The MWW-structured molecular sieve of this invention has good modification potential; for example, it can be prepared into MCM-36 molecular sieve through swelling and pillaring, and into ITQ-2 molecular sieve through swelling and exfoliation. This invention has found that the MCM-49 molecular sieve lacks interlayer hydrogen bonds and cannot be swollen and exfoliated; the MCM-22 molecular sieve prepared using a conventional template agent (hexamethyleneimine), and the MWW-structured molecular sieve provided by this invention, both possess interlayer hydrogen bonds, thus exhibiting swelling and exfoliation capabilities. Compared to MCM-22 molecular sieves made with conventional template agents (hexamethyleneimine), the MWW-structured molecular sieve provided by this invention is easier to delaminate. Specifically, the pH of the alkaline environment required for delamination is closer to neutral, indicating that the interlayer hydrogen bond strength of the MWW-structured molecular sieve provided by this invention is more moderate than that of MCM-22 molecular sieves. This makes it more conducive to preserving the integrity of the sieve's plate-like crystal structure when performing pillaring or delamination modification, improving the stability of the molecular sieve, and reducing the loss of catalytic active sites. Therefore, it is beneficial to improve the catalytic activity and stability of the molecular sieve when applied to reactions such as alkylation, isomerization, or cracking.
[0022] In a specific embodiment of the present invention, the MWW-structured molecular sieve has a high specific surface area, reaching 500 m². 2 ·g or more.
[0023] In a specific embodiment of the present invention, the microporous specific surface area of the MWW structured molecular sieve can reach 350 m². 2 The mesoporous specific surface area of the MWW structured molecular sieve can reach 140 m² / g or more. 2 ·g or more.
[0024] In a specific embodiment of the present invention, the pore volume of the MWW structured molecular sieve can reach 0.60 cm³. 3 ·g or more.
[0025] In a specific embodiment of the present invention, the micropore volume of the MWW molecular sieve can reach 0.16 cm³. 3 ·g or more.
[0026] This invention also provides applications of the above-mentioned MWW-structured molecular sieve in alkylation, isomerization, or cracking catalysis. The catalytic effect of the molecular sieve provided by this invention is no less than that of commercially available MCM-22 molecular sieve. In some specific embodiments, the invented MWW-structured molecular sieve is applied to alkylation reactions, achieving an olefin conversion rate of over 99.97% and a selectivity of over 42%, further reaching over 96%.
[0027] The beneficial effects of this invention include:
[0028] 1. This invention relies on seed crystals and a first template agent to construct the basic layer structure, and relies on a second template agent to construct interlayer hydrogen bonds. Without using traditional template agents such as hexamethyleneimine, piperidine, and piperazine, the product can still have properties similar to MCM-22 molecular sieves and exhibit high catalytic activity.
[0029] 2. The first and second template agents used in this invention are both low-toxicity, readily available organic amines, and are inexpensive. This can greatly improve the operability of MWW structure molecular sieve production and has strong practical application significance. Attached Figure Description
[0030] Figure 1 The image shows the XRD pattern of the seed crystal.
[0031] Figure 2 This is a SEM image of the seed crystal.
[0032] Figure 3 The image shows the XRD pattern of the molecular sieve synthesized in Example 1.
[0033] Figure 4 This is a SEM image of the molecular sieve synthesized in Example 1.
[0034] Figure 5 The image shows the XRD pattern of the molecular sieve synthesized in Example 2.
[0035] Figure 6 This is a SEM image of the molecular sieve synthesized in Example 2.
[0036] Figure 7 The image shows the XRD pattern of the molecular sieve synthesized in Comparative Example 1.
[0037] Figure 8 The image shows the SEM image of the molecular sieve synthesized in Comparative Example 1.
[0038] Figure 9 The image shows the XRD pattern of the molecular sieve synthesized in Comparative Example 2.
[0039] Figure 10 The image shows the SEM image of the molecular sieve synthesized in Comparative Example 2.
[0040] Figure 11 The image shows the XRD pattern of the molecular sieve synthesized in Comparative Example 3.
[0041] Figure 12 The image shows the SEM image of the molecular sieve synthesized in Comparative Example 3.
[0042] Figure 13 This is a TEM image of the molecular sieve synthesized in Comparative Example 1.
[0043] Figure 14 This is a TEM image of the molecular sieve synthesized in Example 1. Detailed Implementation
[0044] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.
[0045] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.
[0046] The raw materials used in the following examples and comparative examples are:
[0047] Silicon sources: silica sol (SiO2 content 40%, content is by mass, the same below), solid silica gel (SiO2 content 95%), white carbon black (SiO2 content 93%), tetraethyl orthosilicate (SiO2 content 98% based on elemental silicon);
[0048] Aluminum sources: sodium aluminate (Al2O3 content 41% based on aluminum element content), aluminum sulfate (Al2O3 content 15% based on aluminum element content), alumina (alumina content 95% based on aluminum element content), boehmite (Al2O3 content 70% based on aluminum element content).
[0049] Alkali source: Sodium hydroxide (99%), potassium hydroxide (99%);
[0050] First template agent: Cyclohexylamine (99%);
[0051] Second template agent: diisopropylamine (99%), di-n-butylamine (99%), diisobutylamine (99%), 1,4-diazabicyclo[2.2.2]octane (99%), 1,6-hexanediamine (99%), N,N,N,N-tetramethyl-1,6-hexanediamine (99%);
[0052] Seed crystals: MCM-22 molecular sieve manufactured by Mobil, which undergoes no calcination process to remove the template agent;
[0053] Water: Deionized water.
[0054] The molecular sieve products used for characterization in the examples and comparative examples were first calcined in air at 540°C and then subjected to BET characterization.
[0055] Example 1
[0056] This embodiment provides an MWW structure molecule, the preparation method of which includes:
[0057] 1. Add 1.87g of sodium hydroxide to 120g of deionized water and stir to dissolve; then add 2.15g of sodium aluminate and stir vigorously for 1 hour to dissolve; then slowly add 9.50g of cyclohexylamine and stir vigorously for 0.5 hours; then slowly add 6.50g of diisopropylamine and stir vigorously for 0.5 hours to obtain an intermediate solution.
[0058] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours. Then add seed crystals, the mass of which is 3% of the silica content in the silica sol, and stir vigorously for 1 hour to obtain a gel. Crystallize the gel at 140℃ for 60 hours. After crystallization, cool to room temperature. Wash and filter the crystallized product with deionized water, and dry it at 120℃ for 4 hours to obtain the molecular sieve product.
[0059] In the above experiment, the content of silicon source was calculated as SiO2, the amount of aluminum source was calculated as Al2O3, and the molar ratio of silicon source to aluminum source was: SiO2 / Al2O3=62.
[0060] Example 2
[0061] This embodiment provides an MWW structure molecule, the preparation method of which includes:
[0062] 1. Dissolve 1.87g sodium hydroxide in 120g deionized water by stirring; add 2.50g sodium aluminate and stir vigorously for 1 hour to dissolve; slowly add 9.00g cyclohexylamine and stir vigorously for 0.5 hours; slowly add 8.00g 1,6-hexanediamine and stir vigorously for 0.5 hours to obtain an intermediate solution.
[0063] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours. Then add seed crystals, the mass of which is 5% of the silica content in the silica sol, and stir vigorously for 1 hour to obtain a gel. Crystallize the gel at 145℃ for 72 hours. After crystallization, cool to room temperature. Wash and filter the crystallized product with deionized water, and dry it at 120℃ for 4 hours to obtain the molecular sieve product.
[0064] In the above experiment, the content of silicon source was calculated as SiO2, and the amount of aluminum source was calculated as Al2O3. The molar ratio of silicon source to aluminum source was: SiO2 / Al2O3 = 53.3.
[0065] Example 3
[0066] This embodiment provides an MWW structure molecule, the preparation method of which includes:
[0067] 1. Add 1.95g sodium hydroxide to 130g deionized water and stir to dissolve; add 2.33g sodium aluminate and stir vigorously for 1 hour; slowly add 9.00g cyclohexylamine and stir vigorously for 0.5 hours; slowly add 9.00g 1,4-diazabicyclo[2.2.2]octane and stir vigorously for 0.5 hours to obtain an intermediate solution.
[0068] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours. Then add seed crystals, the mass of which is 5% of the silica content in the silica sol, and stir vigorously for 1 hour to obtain a gel. Crystallize the gel at 140℃ for 72 hours. After crystallization, cool to room temperature. Wash the crystallized product with deionized water, filter, and air dry naturally for 48 hours to obtain the molecular sieve product.
[0069] In the above experiment, the content of silicon source was calculated as SiO2, the amount of aluminum source was calculated as Al2O3, and the molar ratio of silicon source to aluminum source was: SiO2 / Al2O3=57.2.
[0070] Example 4
[0071] This embodiment provides an MWW structure molecule, the preparation method of which includes:
[0072] 1. Add 1.93g of sodium hydroxide to 150g of deionized water and stir to dissolve; add 1.50g of sodium aluminate and stir vigorously for 1 hour; slowly add 12.25g of cyclohexylamine and stir vigorously for 0.5 hours; slowly add 8.50g of N,N,N,N-tetramethyl-1,6-hexanediamine and stir vigorously for 0.5 hours to obtain an intermediate solution.
[0073] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours; then add 10% seed crystals and stir vigorously for 1 hour to obtain a gel. Crystallize the gel at 140℃ for 100 hours. After crystallization, cool to room temperature. Wash and filter the product with deionized water, and dry at 120℃ for 4 hours to obtain the molecular sieve product.
[0074] In the above experiment, the content of silicon source was calculated as SiO2, the amount of aluminum source was calculated as Al2O3, and the molar ratio of silicon source to aluminum source was: SiO2 / Al2O3=88.9.
[0075] Example 5
[0076] This embodiment provides an MWW-structured molecule, the preparation method of which includes:
[0077] 1. Add 2.21g of sodium hydroxide to 175g of deionized water and stir to dissolve; add 1.25g of sodium aluminate and stir vigorously for 1 hour; slowly add 7.55g of cyclohexylamine and stir vigorously for 0.5 hours; slowly add 10.50g of diisobutylamine and stir vigorously for 0.5 hours to obtain an intermediate solution.
[0078] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours. Add seed crystals, the mass of which is 15% of the silica content in the silica sol, and stir vigorously for 1 hour to obtain a gel. Crystallize the gel at 140℃ for 120 hours. After crystallization, cool to room temperature. Wash and filter the product with deionized water, and air dry naturally for 48 hours to obtain the molecular sieve product.
[0079] In the above experiment, the content of silicon source was calculated as SiO2, the amount of aluminum source was calculated as Al2O3, and the molar ratio of silicon source to aluminum source was: SiO2 / Al2O3=106.6.
[0080] Comparative Example 1
[0081] This comparative example provides a molecular sieve, the preparation method of which includes:
[0082] 1. Add 1.95g sodium hydroxide to 130g deionized water and stir to dissolve; add 2.33g sodium aluminate and stir vigorously for 1 hour; slowly add 9.00g cyclohexylamine and stir vigorously for 0.5 hours to obtain an intermediate solution.
[0083] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours. Add seed crystals, the mass of which is 5% of the silica content in the silica sol, and stir vigorously for 1 hour to obtain a gel. Crystallize the gel at 140℃ for 72 hours. After crystallization, cool to room temperature. Wash and filter the product with deionized water, and air dry naturally for 48 hours to obtain the molecular sieve product.
[0084] Comparative Example 2
[0085] This comparative example provides a molecular sieve, the preparation method of which includes:
[0086] 1. Add 1.87g of sodium hydroxide to 120g of deionized water and stir to dissolve; add 2.15g of sodium aluminate and stir to dissolve. Continue stirring vigorously for 1 hour. Slowly add 19.0g of hexamethyleneimine (molar ratio of template agent to silicon source is 0.35:1) and continue stirring vigorously for 0.5 hours to obtain an intermediate solution;
[0087] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours to obtain a crystallized gel. Crystallize the gel at 155℃ for 60 hours. After crystallization, cool to room temperature. Wash and filter the product with deionized water, and dry at 120℃ for 4 hours to obtain the molecular sieve product.
[0088] The method uses hexamethyleneimine, a typical template agent for preparing MCM-22 molecular sieves. Although this comparative example can obtain pure-phase MCM-22 molecular sieves, the amount of hexamethyleneimine used as the template agent is large, and the template agent is expensive and highly toxic.
[0089] Comparative Example 3
[0090] This comparative example provides a molecular sieve, the preparation method of which includes:
[0091] 1. Add 1.87g of sodium hydroxide to 120g of deionized water and stir to dissolve. Add 2.15g of sodium aluminate and stir to dissolve. Continue stirring vigorously for 1 hour. Slowly add 9.50g of cyclohexylamine and 9.50g of hexamethyleneimine, and continue stirring vigorously for 0.5 hours to obtain an intermediate solution.
[0092] 2. Slowly add 80g of silica sol to the intermediate solution and stir vigorously for 3 hours to obtain a crystallized gel. Crystallize the gel at 155℃ for 60 hours. After crystallization, cool to room temperature. Wash and filter the product with deionized water, and dry at 120℃ for 4 hours to obtain the molecular sieve product.
[0093] Test Example 1
[0094] This test case characterizes the structure of the above embodiments and comparative examples.
[0095] Figure 1 , Figure 2 The images shown are XRD patterns and SEM images of the seed crystals (MCM-22 molecular sieve sold by Mobil) used in the above examples and comparative examples, respectively.
[0096] Figure 3 , Figure 4 The images shown are the XRD patterns and SEM images of the molecular sieve products from Example 1. Figure 3 , Figure 4 It can be seen that the molecular sieve product prepared in Example 1 has typical MWW structural characteristic peaks, and the morphology of the molecular sieve product is a flower-like cluster of nanosheets.
[0097] Figure 5 , Figure 6 The images shown are the XRD patterns and SEM images of the molecular sieve products from Example 2. Figure 5 , Figure 6It can be seen that the molecular sieve product prepared in Example 2 has typical MWW structural characteristic peaks, and the morphology of the molecular sieve product is a flower-like cluster of nanosheets.
[0098] XRD and SEM characterization of the molecular sieve products of Examples 3, 4, and 5 also showed that the above samples had typical MWW structural characteristic peaks, and the morphology of the molecular sieve products was a flower-like cluster of nanosheets.
[0099] Figure 7 , Figure 8 The images show the XRD patterns and SEM images of the molecular sieve product from Comparative Example 1, respectively. Figure 7 , Figure 8 As can be seen, the molecular sieve product prepared in Comparative Example 1 has typical MWW structural characteristic peaks and can be further subdivided into MCM-49 molecular sieve. Furthermore, the morphology of this molecular sieve product exhibits ordered stacking of nanosheets.
[0100] Figure 9 , Figure 10 The images show the XRD pattern and SEM image of the molecular sieve product of Comparative Example 2, respectively. It can be seen that the molecular sieve product prepared in Comparative Example 2 exhibits typical MWW structural characteristic peaks and can be further subdivided into MCM-22 molecular sieves, with the morphology of the molecular sieve being nanosheets.
[0101] Figure 11 , Figure 12 The images show the XRD patterns and SEM images of the molecular sieve product of Comparative Example 3, respectively. It can be seen that the molecular sieve product prepared in Comparative Example 3 exhibits typical MWW structural characteristic peaks. The molecular sieve product is a mixture of MCM-22 and MCM-49 molecular sieves, and the morphology of the molecular sieve is a stacked nanosheet structure.
[0102] Comparing the XRD results of the molecular sieve products from Examples 1 to 5 with those from Comparative Example 1, it can be seen that the molecular sieve products from Examples 1 to 5 have independent characteristic peaks at 7.09° (corresponding to the 002 crystal plane) and 7.18°, respectively. These two characteristic peaks indicate that there is a significant interlayer spacing between the 002 crystal planes in the molecular sieve products. This is because the second template agent constructs interlayer hydrogen bonds and generates a certain degree of retardation between adjacent 002 crystal planes, thus creating a significant distance between adjacent crystal planes. In contrast, the XRD pattern of the product from Comparative Example 1 only shows a significant characteristic peak at 7.18° and no significant characteristic peak at 7.09°. This is because the 002 crystal planes in the product from Comparative Example 1 are stacked and do not have a significant interlayer spacing; the interlayer bonding in the product from Comparative Example 1 consists of condensed oxygen bridges.
[0103] The hexamethyleneimine used in Comparative Example 2 is a typical template agent for preparing MCM-22 molecular sieves, and the molecular sieve obtained in Comparative Example 2 is a pure-phase MCM-22 molecular sieve. Comparing the XRD results of the molecular sieve products from Examples 1 to 5 with those of Comparative Example 2 shows that the molecular sieves from Examples 1 to 5 have structures similar to MCM-22 molecular sieves, further confirming that the molecular sieve of this application, like MCM-22, possesses interlayer hydrogen bonds.
[0104] The above comparison results demonstrate that: using cyclohexylamine alone as a template agent yields MCM-49 molecular sieve; while using cyclohexylamine and a second template agent as template agents, MWW-structured molecular sieves can be prepared, which have interlayer hydrogen bonds and a structure similar to that of MCM-22 molecular sieve produced by Mobil.
[0105] Comparing the product compositions of Comparative Example 3 and Example 1, it can be seen that although using hexamethyleneimine and cyclohexylamine as a composite template agent can synthesize a pure-phase MWW structured molecular sieve, the product of Comparative Example 3 is a mixture of MCM-22 and MCM-49 molecular sieves, and a pure-phase MCM-22 structured molecular sieve cannot be obtained. The reason why the composite template agent of hexamethyleneimine and cyclohexylamine cannot obtain a pure-phase molecular sieve is that when cyclohexylamine is used to replace a certain proportion of hexamethyleneimine, cyclohexylamine does not have the ability to construct interlayer hydrogen bonds, and the concentration of hexamethyleneimine is too low to construct enough hydrogen bonds. Therefore, only a mixture of the two molecular sieves can be obtained, and a single pure-phase molecular sieve cannot be obtained.
[0106] Figure 13 This is a TEM image of the molecular sieve product prepared in Comparative Example 1. Figure 14 This is a TEM image of the molecular sieve product prepared in Example 1. (Comparison) Figure 13 , Figure 14 It can be seen that the molecular sieve of Comparative Example 1 has obvious stacking of the base layer, and the sheet thickness is about 20 nm; in contrast, the molecular sieve of Example 1 has a reduced number of base layer stacks, and the molecular sieve sheet thickness is about 10 nm, which is significantly reduced compared to Comparative Example 1.
[0107] Test Example 2
[0108] This test example provides the specific surface area and pore volume results of the molecular sieve products of Examples 1 to 5 and Comparative Example 1, measured by BET. The specific results are shown in Table 1. Wherein, S... BET S is the specific surface area. mic S represents the surface area of the micropores. ext V is the surface area of the mesopores. pore V is the volume of the pore. mic This represents the micropore volume.
[0109] Table 1
[0110]
[0111] As can be seen from Table 1, the molecular sieves prepared in Examples 1 to 5 of the present invention have a larger micropore specific surface area, mesopore specific surface area, total specific surface area and total pore volume than the molecular sieve products prepared in Comparative Examples 1 to 3, and the micropore volume of the molecular sieves prepared in Examples 1 to 5 is not lower than that of the molecular sieve products prepared in Comparative Examples 1 to 3.
[0112] Compare the data in Table 1 with... Figure 13 , Figure 14 The results show that the preparation method provided by this invention, by adding a second template agent, can utilize the N atoms sp in the second template agent. 3 The orbital holes form hydrogen bonds with the hydrogen in the silanol groups, resulting in a molecular sieve that not only possesses the MWW topology but also shares similarities with the MCM-22 molecular sieve in terms of interlayer hydrogen bonds, thus exhibiting the characteristics of the MCM-22 molecular sieve. Furthermore, the total specific surface area and total pore volume of the molecular sieve of this invention are significantly increased. In addition, the molecular sieve product prepared by this invention has a lower stacking number and smaller lamellar thickness, and the stacking morphology of the molecular sieve is altered compared to the MCM-49 molecular sieve.
[0113] Combining the results of Test Examples 1 and 2, it can be seen that Comparative Example 1, using cyclohexylamine as a template agent, can directly synthesize a highly crystalline, pure-phase MWW-structured molecular sieve, which can be further subdivided into MCM-49 molecular sieves. However, since cyclohexylamine cannot form interlayer hydrogen bonds, it is only suitable as a template agent for synthesizing MCM-49 molecular sieves and cannot synthesize other types of MWW-structured molecular sieves. Comparative Example 3, using cyclohexylamine to replace part of hexamethyleneimine as a composite template agent, also fails to form sufficient interlayer hydrogen bonds. Therefore, only a mixture of MCM-22 and MCM-49 molecular sieves can be prepared, and a pure-phase molecular sieve with the MCM-22 structure cannot be obtained.
[0114] Example 6
[0115] This embodiment provides the application of the molecular sieve product of Example 1 in catalytic alkylation reaction.
[0116] The molecular sieve product from Example 1 was calcined at 540°C for 5 hours in air to remove the template agent. Then, it was subjected to ammonium exchange in a 1 mol / L ammonium nitrate solution at 80°C for 2 hours, and then calcined again at 540°C in air for 4 hours to obtain the H-type molecular sieve.
[0117] 90g of the above-mentioned H-type molecular sieve was mixed evenly with 15g of pseudoboehmite. While mixing, 55g of nitric acid solution was gradually added. The mixture was extruded into cylindrical catalysts with a diameter of 2.0mm, and then cut into cylindrical catalysts with a length of 2.5mm. The catalysts were air-dried at room temperature for 24 hours, and then calcined at 550℃ for 6 hours to obtain the finished catalyst product.
[0118] Take 2g of the above-mentioned catalyst product and load it into a fixed-bed reactor, then introduce a mixture of benzene and ethylene. The reaction conditions are: benzene-to-ethylene ratio 5, reaction temperature 330℃, reaction pressure 1.4MPa, and mass hourly space velocity 2.0h⁻¹. -1 .
[0119] The reaction results were as follows: after 500 h of reaction, the olefin conversion rate was 99.99% and the ethylbenzene selectivity was 96.21%.
[0120] Example 7
[0121] This embodiment provides the application of the molecular sieve product of Example 2 in catalytic alkylation reaction.
[0122] The molecular sieve product from Example 2 was calcined at 540°C for 5 hours in air to remove the template agent. Then, it was subjected to ammonium exchange in a 1 mol / L ammonium nitrate solution at 80°C for 2 hours, and then calcined again at 540°C in air for 4 hours to obtain the H-type molecular sieve.
[0123] 90g of the above-mentioned H-type molecular sieve was mixed evenly with 15g of pseudoboehmite. While mixing, 55g of nitric acid solution was gradually added. The mixture was extruded into cylindrical catalysts with a diameter of 2.0mm, and then cut into cylindrical catalysts with a length of 2.5mm. The catalysts were air-dried at room temperature for 24 hours, and then calcined at 550℃ for 6 hours to obtain the finished catalyst product.
[0124] Take 2g of the above-mentioned catalyst product and load it into a fixed-bed reactor, then introduce a mixture of benzene and propylene. The reaction conditions are: benzene-to-propylene ratio 4, reaction temperature 150℃, reaction pressure 2.5MPa, and mass hourly space velocity 3.0h⁻¹. -1 .
[0125] The reaction results were as follows: after 300 h of reaction, the olefin conversion rate was 99.97% and the selectivity of cumene was 99.20%.
[0126] Example 8
[0127] This embodiment provides the application of the molecular sieve product of Example 3 in catalytic alkylation reaction.
[0128] The molecular sieve product from Example 3 was calcined at 540°C for 5 hours in air to remove the template agent. Then, it was subjected to ammonium exchange in a 1 mol / L ammonium nitrate solution at 80°C for 2 hours, and then calcined again at 540°C in air for 4 hours to obtain the H-type molecular sieve.
[0129] 90g of the above-mentioned H-type molecular sieve was mixed evenly with 15g of pseudoboehmite. While mixing, 55g of nitric acid solution was gradually added. The mixture was extruded into cylindrical catalysts with a diameter of 2.0mm, and then cut into cylindrical catalysts with a length of 2.5mm. The catalysts were air-dried at room temperature for 24 hours, and then calcined at 550℃ for 6 hours to obtain the finished catalyst product.
[0130] Take 2g of the above-mentioned catalyst product and load it into a fixed-bed reactor. A mixture of benzene and n-dodecene is then introduced. The reaction conditions are: benzene-to-benzene ratio 15, reaction temperature 150℃, reaction pressure 3.0MPa, and mass hourly space velocity 2.0h⁻¹. -1 .
[0131] The reaction results were as follows: after 300 h of reaction, the olefin conversion rate was 99.97% and the 2-alkylbenzene selectivity was 42.01%.
[0132] Comparative Example 4
[0133] This comparative example provides the application of the molecular sieve product of Comparative Example 1 in catalytic alkylation reactions.
[0134] The molecular sieve of Comparative Example 1 was calcined at 540℃ for 5 hours in air to remove the template agent. Then, it was subjected to ammonium exchange in 1 mol / L ammonium nitrate solution at 80℃ for 2 hours, and calcined again at 540℃ in air for 4 hours to obtain the H-type molecular sieve.
[0135] 90g of the above-mentioned H-type molecular sieve was mixed evenly with 15g of pseudoboehmite. While mixing, 55g of nitric acid solution was gradually added. The mixture was extruded into cylindrical catalysts with a diameter of 2.0mm, and then cut into cylindrical catalysts with a length of 2.5mm. The catalysts were air-dried at room temperature for 24 hours, and then calcined at 550℃ for 6 hours to obtain the finished catalyst product.
[0136] Take 2g of the above-mentioned catalyst product and load it into a fixed-bed reactor. A mixture of benzene and n-dodecene is then introduced. The reaction conditions are: benzene-to-benzene ratio 15, reaction temperature 150℃, reaction pressure 3.0MPa, and mass hourly space velocity 2.0h⁻¹. -1 .
[0137] The reaction results were as follows: after 100 h of reaction, the olefin conversion rate was 76.32% and the 2-alkylbenzene selectivity was 45.03%.
[0138] Comparing the results of Comparative Example 4 with those of Examples 6 to 8, it can be seen that the catalysts in Examples 6 to 8 exhibit higher olefin conversion and cumene selectivity. This is because the MCM-49 molecular sieve prepared in Comparative Example 1 lacks interlayer hydrogen bonds, and the monolayers tend to stack, forming condensed oxygen bridges, resulting in a high degree of stacking. In contrast, the molecular sieves prepared in the examples possess interlayer hydrogen bonds. These hydrogen bonds, along with the template agents used to construct them, have steric hindrance effects between the layers, preventing stacking between the molecular sieve layers. Therefore, the degree of stacking in the molecular sieves of the examples is low. Since the degree of stacking of the molecular sieves in the examples is lower than that of the molecular sieve in Comparative Example 1, the sheet thickness of the molecular sieves prepared in Examples 1 to 3 is less than that of the MCM-49 molecular sieve in Comparative Example 1. This results in a greater number of exposed surface catalytic active sites per unit mass of catalyst, leading to higher catalytic activity and avoiding deactivation due to blockage during the reaction, thus extending catalyst lifetime.
[0139] As can be seen from the above, the preparation method provided by the present invention can synthesize MWW structure molecular sieves with interlayer hydrogen bonds without omitting traditional template agents such as hexamethyleneimine, piperidine, and piperazine. These molecular sieves have similar properties to MCM-22 molecular sieves and have high catalytic activity.
Claims
1. A method for preparing MWW-structured molecular sieves, wherein, The preparation method includes: An aluminum source, water, an alkali source, a first template agent, a second template agent, a silicon source, and seed crystals are mixed to form a gel, which is then crystallized to obtain the MWW structured molecular sieve. Wherein, the first template agent includes cyclohexylamine, and the second template agent includes one or more of the following: diisopropylamine, di-n-butylamine, diisobutylamine, 1,4-diazabicyclo[2.2.2]octane, 1,6-hexanediamine, and N,N,N,N-tetramethyl-1,6-hexanediamine; The molar ratio of the first template agent to the second template agent is 0.5-20:1; The seed crystal is a molecular sieve with an MWW topology; Wherein, the alkali source is denoted as MOH, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the alkali source is calculated as M2O, the sum of the first template agent and the second template agent is denoted as T, and the chemical composition of the gel satisfies the following molar ratio range: Al2O3 / SiO2=0.005-0.05, M2O / SiO2=0.03-0.50, T / SiO2=0.10-0.75, H2O / SiO2=8-120; The mass ratio of seed crystal to silicon source, based on dry weight, satisfies: seed crystal / SiO2 = 0.01-0.25; The crystallization temperature is 120-170℃, and the crystallization time is 12-120h.
2. The preparation method according to claim 1, wherein, The chemical composition of the gel satisfies the following molar ratio range: H2O / SiO2 = 15-120.
3. The preparation method according to claim 1, wherein, The silicon source includes one or more of silicon dioxide, silicates, and silicate esters.
4. The preparation method according to claim 1, wherein, The silicon source includes one or more of the following: silica sol, solid silica gel, fumed silica, water glass, and tetraethyl orthosilicate.
5. The preparation method according to claim 1, wherein, The aluminum source includes one or more of aluminates, aluminum sulfate, alumina, and boehmite.
6. The preparation method according to claim 1, wherein, The seed crystals include MCM-22 molecular sieve and / or MCM-49 molecular sieve.
7. The preparation method according to claim 1, wherein, The alkali source includes sodium hydroxide and / or potassium hydroxide.
8. The preparation method according to any one of claims 1-7, wherein, The preparation method includes: An intermediate solution is obtained by mixing an aluminum source, water, an alkali source, a first template agent, and a second template agent. A silicon source and seed crystals are added to the intermediate solution, and the mixture is mixed to form a gel. The gel is then crystallized to obtain the MWW structured molecular sieve.
9. An MWW-structured molecular sieve, which is obtained by the preparation method according to any one of claims 1-8.
10. The MWW-structured molecular sieve according to claim 9, wherein, The specific surface area of the MWW structured molecular sieve is 500 m². 2 ·g or more.
11. The MWW-structured molecular sieve according to claim 9, wherein, The specific surface area of the micropores in the MWW structured molecular sieve is 350 m². 2 The mesoporous specific surface area of the MWW structured molecular sieve is 140 m² / g or more. 2 ·g or more.
12. The MWW-structured molecular sieve according to claim 9, wherein, The pore volume of the MWW-structured molecular sieve is 0.60 cm³. 3 ·g or more.
13. The MWW-structured molecular sieve according to claim 9, wherein, The micropore volume of the MWW-structured molecular sieve is 0.16 cm³. 3 ·g or more.
14. The use of the MWW structured molecular sieve according to any one of claims 9-13 in the catalysis of alkylation, isomerization or cracking reactions.