A method for preparing a polycationic structure directing agent and a ZSM-11 / ZSM-5 intergrowth molecular sieve

Abstract

The application provides a kind of polycation structure directing agent and the preparation method of ZSM-11 / ZSM-5 intergrowth molecular sieve, it is related to molecular sieve technical field.The polycation structure directing agent provided by the application is quaternary ammonium type cationic polymer with long chain structure.ZSM-11 / ZSM-5 intergrowth molecular sieve (with fixed intergrowth ratio) with controllable ZSM-11 content can be prepared by using the polycation structure directing agent, and multi-level pore structure (including micropore and mesopore) with better diffusion performance is formed during synthesis process, and the crystal grain size is 150-300nm;And the polycation structure directing agent can direct the generation of ZSM-11 / ZSM-5 intergrowth molecular sieve in a wide silicon-aluminum ratio window (50-infinity);In addition, the polycation structure directing agent is a single directing agent, without controlling the ratio between each directing agent as in the co-template method, and without adding pore-forming agent when forming multi-level pore structure.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, and in particular to a method for preparing a polycationic structure directing agent and a ZSM-11 / ZSM-5 symbiotic molecular sieve. Background Technology

[0002] Molecular sieves are microporous aluminosilicate crystals with a framework structure formed by TO4 (T = Si, Al, or P, etc.) tetrahedra sharing O atoms. This structure endows them with excellent ion exchange capacity, hydrothermal stability, strong acidity, and unique molecularly selective adsorption and shape-selective catalysis properties. In recent decades, symbiotic molecular sieves have gradually attracted widespread attention from academia and industry. The competitive growth of different crystals leads to frequent stacking defects in various topologies, while the stacking order between phase layers easily leads to symbiosis. Symbiotic molecular sieve crystals exhibit unique synergistic effects and catalytic advantages in the fields of adsorption, separation, and catalysis.

[0003] ZSM-5 (MFI) and ZSM-11 (MEL) molecular sieves, as important members of the five-membered ring zeolite family, have closely related framework structures that can be described by different stacking arrangements of the same five-membered ring chains. In the ZSM-5 structure, adjacent five-membered ring chains are connected by centrosymmetry, while in the ZSM-11 structure, they are connected by mirror symmetry. These subtle differences in pore structure make the preparation of ZSM-11 / ZSM-5 co-existing molecular sieves possible; this structure was first reported by ExxonMobil in 1979. Currently, ZSM-11 / ZSM-5 co-existing molecular sieves have been commercially applied in the gas-phase alkylation of benzene with catalytic cracking tail gas to produce ethylbenzene. They also exhibit excellent catalytic performance in the catalytic cracking of n-decane and methanol-to-hydrocarbon reactions.

[0004] The preparation of the ZSM-11 / ZSM-5 symbiotic structure has attracted widespread interest from researchers due to its unique catalytic and adsorption properties. ZSM-11 / ZSM-5 symbiotic molecular sieves are often synthesized using tetrabutylammonium (TBA) and tetrapropylammonium (TPA) as structure-directing agents, employing a co-template method. However, because ZSM-5 has a more stable lattice, its structure often becomes the dominant polymorph, and the ZSM-11 structure only appears when the TBA content exceeds 90%. The synthesis process requires precise control of the TBA-TPA ratio, making it difficult to manage and resulting in unstable ZSM-11 / ZSM-5 symbiotic ratios and low ZSM-11 content. Furthermore, the ZSM-11 / ZSM-5 symbiotic molecular sieve obtained by this method has a single microporous structure, limiting its diffusion performance and affecting its catalytic performance. Introducing common pore-forming agents can also affect the formation of the symbiotic structure, making the synthesis of symbiotic hierarchical porous molecular sieves a significant challenge. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing a polycationic structure-directing agent and a ZSM-11 / ZSM-5 symbiotic molecular sieve. Using the polycationic structure-directing agent provided by this invention, ZSM-11 / ZSM-5 symbiotic molecular sieves with controllable ZSM-11 content can be prepared, and a hierarchical porous structure with superior diffusion performance is formed during the synthesis process.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a polycationic directed agent having the structure shown in Formula I:

[0008]

[0009] In the structure shown in Formula I, X is Br or OH, and n is an integer from 5 to 20.

[0010] This invention provides a method for preparing the polycationic directed agent described in the above technical solution, comprising the following steps:

[0011] A nucleophilic addition reaction was carried out by mixing di-n-butylamine, octanoyl chloride and an organic solvent to give N,N,N',N'-tetrabutyl-1,8-octanoyldiamide;

[0012] The N,N,N',N'-tetrabutyl-1,8-octadiamide was mixed with lithium aluminum hydride and an organic solvent for a reduction reaction to obtain N,N,N',N'-tetrabutyl-1,8-octadiamine;

[0013] The N,N,N',N'-tetrabutyl-1,8-octanediamine was mixed with 1,8-dibromooctane and an organic solvent to carry out a nucleophilic substitution polymerization reaction to obtain a polycationic directed agent with the structure shown in Formula I when X is Br.

[0014] When X is Br, the polycationic directed agent of Formula I is subjected to ion exchange through a strongly basic anion exchange resin to obtain the polycationic directed agent of Formula I when X is OH.

[0015] Preferably, the molar ratio of di-n-butylamine to octanyl chloride is 4:1, and the nucleophilic addition reaction is carried out at room temperature for 24–48 hours.

[0016] Preferably, the molar ratio of N,N,N',N'-tetrabutyl-1,8-octadiamide to lithium aluminum hydride is 1:3, and the reduction reaction is carried out at a temperature of 60–100°C for 24–48 hours.

[0017] Preferably, the molar ratio of N,N,N',N'-tetrabutyl-1,8-octanediamine to 1,8-dibromooctane is 1:1, and the nucleophilic substitution polymerization reaction is carried out at a temperature of 60–100°C for a time of 24–96 h.

[0018] This invention provides a method for preparing ZSM-11 / ZSM-5 symbiotic molecular sieves, comprising the following steps:

[0019] A structure-directing agent, a silicon source, an aluminum source, an alkali source, and water are mixed and subjected to hydrothermal crystallization to obtain a crystallized product. The structure-directing agent is the polycationic structure-directing agent described in the above technical solution, and the alkali source is an alkali metal hydroxide. The silicon source is calculated as SiO2, the aluminum source as Al2O3, the alkali source as an alkali metal element, and the structure-directing agent as a structural unit. The molar ratio of the silicon source, aluminum source, structure-directing agent, alkali source, and water is 1:(0~0.04):(0.05~0.50):(0.02~0.50):(10~150).

[0020] The crystallized product was calcined to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve.

[0021] Preferably, the silicon source includes one or more of tetraethyl orthosilicate, sodium silicate, fumed silica, silica sol, and silica fume; the aluminum source includes one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum hydroxide, sodium aluminate, boehmite, and aluminum isopropoxide; and the alkali source includes one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0022] Preferably, the hydrothermal crystallization temperature is 110–190°C and the time is 3–14 days.

[0023] Preferably, the ZSM-11 / ZSM-5 symbiotic molecular sieve has micropores and mesopores, a particle size of 150-300 nm, and a silicon-aluminum molar ratio greater than or equal to 50.

[0024] Preferably, the symbiotic ratio of ZSM-11 molecular sieve to ZSM-5 molecular sieve in the ZSM-11 / ZSM-5 symbiotic molecular sieve is 80:20.

[0025] This invention provides a polycationic directed agent having the structure shown in Formula I. The polycationic directed agent provided by this invention is a quaternary ammonium cationic polymer with a long-chain structure. ZSM-11 / ZSM-5 symbiotic molecular sieves were prepared using the aforementioned polycationic structure-directing agent. As a structure-directing agent, the polycationic structure-directing agent can prepare ZSM-11 / ZSM-5 symbiotic molecular sieves with controllable ZSM-11 content (with a fixed symbiotic ratio). During synthesis, it can generate a hierarchical porous structure (including micropores and mesopores) with superior diffusion performance. The resulting symbiotic molecular sieve size can be reduced to 150–300 nm, resulting in better mass transfer. Furthermore, the polycationic structure-directing agent can guide the formation of ZSM-11 / ZSM-5 symbiotic molecular sieves within a wide silica-to-alumina ratio window (50–∞). In addition, the polycationic structure-directing agent is a single-agent agent, eliminating the need to control the ratio between different agents as in the co-template method. Since it can also act as a pore-forming agent supporting the mesoporous structure, no additional pore-forming agent is required to form the mesoporous structure. The molecular sieve synthesis process is easier to control, and the resulting molecular sieve has a uniform and controllable microstructure.

[0026] This invention provides a method for preparing ZSM-11 / ZSM-5 symbiotic molecular sieves. The ZSM-11 / ZSM-5 symbiotic molecular sieves prepared using this method have a fixed symbiotic ratio (80:20 between ZSM-11 and ZSM-5 molecular sieves) and a hierarchical pore structure (including micropores and mesopores). The crystallites are between 150 and 300 nm. The hierarchical pore structure provides better diffusion performance, which will help improve the catalytic activity, selectivity, and anti-carbon deposition performance of the catalyst. Furthermore, the ZSM-11 / ZSM-5 symbiotic molecular sieves have a large silica-to-alumina ratio window (50 to ∞). Attached Figure Description

[0027] Figure 1 To implement step 1, the N,N,N',N'-tetrabutyl-1,8-octadiamide prepared was... 1 H NMR spectrum (a) and 13 C NMR spectrum (b);

[0028] Figure 2 The N,N,N',N'-tetrabutyl-1,8-octanediamine prepared in Example 1 1 H NMR spectrum (a) and 13 C NMR spectrum (b);

[0029] Figure 3 The polycationic directed agent [(Bu)2-C8] prepared in Example 1 n (Br) 1 H NMR spectrum (a) and 13C NMR spectrum (b);

[0030] Figure 4 The image shows the XRD pattern of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 3. Figure 4 From left to right, the second and third small images are magnified views of the first small image.

[0031] Figure 5 The images show FE-SEM images of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 3 at different magnifications (scale bars in the figures are 5 μm, 2 μm, 1 μm, and 500 nm, respectively).

[0032] Figure 6 The image shows the XRD pattern of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 4. Figure 6 From left to right, the second and third small images are magnified views of the first small image.

[0033] Figure 7 FE-SEM images of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 4 at different magnifications (5μm, 2μm, 1μm, 500nm);

[0034] Figure 8 The image shows the XRD pattern of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 5. Figure 8 From left to right, the second and third small images are magnified views of the first small image.

[0035] Figure 9 The images show FE-SEM images of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 5 at different magnifications (scale bars in the figures are 5 μm, 2 μm, 1 μm, and 500 nm, respectively).

[0036] Figure 10 The image shows the XRD pattern of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 6. Figure 10 From left to right, the second and third small images are magnified views of the first small image.

[0037] Figure 11 The images show FE-SEM images of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 6 at different magnifications (scale bars in the figures are 5 μm, 2 μm, 1 μm, and 500 nm, respectively).

[0038] Figure 12 The N2 physical adsorption isotherm of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 6 (inset shows the pore size distribution);

[0039] Figure 13Mercury intrusion curves of the ZSM-11 / ZSM-5 symbiotic molecular sieve prepared in Example 6 using mercury intrusion porosimetry (inset shows pore size distribution). Detailed Implementation

[0040] This invention provides a polycationic directed agent having the structure shown in Formula I:

[0041]

[0042] In the structure shown in Formula I, X is Br or OH, and n is an integer from 5 to 20.

[0043] In this invention, n can be 5, 10, 12, 15 or 20.

[0044] In this invention, when X is Br, the chemical formula of the polycationic directed agent with the structure shown in Formula I is [-N + (CH2CH2CH2CH3)2-(CH2)8-] n [Br - ] n (Abbreviated as [(Bu)2-C8)) n (Br)), when X is OH, the chemical formula of the polycationic directed agent with the structure shown in Formula I is [-N + (CH2CH2CH2CH3)2-(CH2)8-] n [OH - ] n (Abbreviated as [(Bu)2-C8)) n (OH)).

[0045] The polycationic structure-directing agent provided by this invention is a quaternary ammonium cationic polymer with a long-chain structure. Each individual quaternary ammonium salt structural unit has a TBA (tetrabutylammonium)-like structure, and the overall structure is equivalent to a linear polymeric cation formed by linking TBA-like structures through C-C bonds. The polycationic structure-directing agent can construct a multi-level structure while controlling the formation of ZSM-5 / ZSM-11 symbiotic structures.

[0046] This invention provides a method for preparing the polycationic directed agent described in the above technical solution, comprising the following steps:

[0047] A nucleophilic addition reaction was carried out by mixing di-n-butylamine, octanoyl chloride and an organic solvent to give N,N,N',N'-tetrabutyl-1,8-octanoyldiamide;

[0048] The N,N,N',N'-tetrabutyl-1,8-octadiamide was mixed with lithium aluminum hydride and an organic solvent for a reduction reaction to obtain N,N,N',N'-tetrabutyl-1,8-octadiamine;

[0049] The N,N,N',N'-tetrabutyl-1,8-octanediamine was mixed with 1,8-dibromooctane and an organic solvent to carry out a nucleophilic substitution polymerization reaction to obtain a polycationic directed agent with the structure shown in Formula I when X is Br.

[0050] When X is Br, the polycationic directed agent of Formula I is subjected to ion exchange through a strongly basic anion exchange resin to obtain the polycationic directed agent of Formula I when X is OH.

[0051] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known in the art.

[0052] This invention involves mixing di-n-butylamine, octanoyl chloride, and an organic solvent to perform a nucleophilic addition reaction, yielding N,N,N',N'-tetrabutyl-1,8-octanoyldiamide.

[0053] In this invention, the molar ratio of di-n-butylamine to octanyl chloride is preferably 4:1; the organic solvent is preferably diethyl ether. This invention does not have specific requirements on the amount of organic solvent used, as long as the raw materials are fully dissolved. In this invention, the preferred method for mixing the di-n-butylamine, octanyl chloride, and organic solvent is as follows: add the organic solvent and di-n-butylamine to the reaction vessel, incubate in an ice bath for 1 hour, and then slowly add octanyl chloride. In this invention, the temperature of the nucleophilic addition reaction is preferably room temperature, and the time is preferably 24–48 hours, which can be 24, 36, or 48 hours; the nucleophilic addition reaction is preferably carried out under stirring conditions. In this invention, the reaction formula for the nucleophilic addition reaction is shown in Formula A (where compound R1 in Formula A is N,N,N',N'-tetrabutyl-1,8-octanyldiamide):

[0054]

[0055] After the nucleophilic addition reaction is completed, the present invention preferably filters the obtained reaction solution to obtain a clear solution, washes the clear solution three times with 5 wt% NaHCO3 solution, dries it with anhydrous magnesium sulfate for 24 h, and then removes the solvent by rotary evaporation to obtain N,N,N',N'-tetrabutyl-1,8-octadiamide.

[0056] After obtaining N,N,N',N'-tetrabutyl-1,8-octadiamide, the present invention performs a reduction reaction by mixing the N,N,N',N'-tetrabutyl-1,8-octadiamide with lithium aluminum hydride and an organic solvent to obtain N,N,N',N'-tetrabutyl-1,8-octadiamine.

[0057] In this invention, the molar ratio of N,N,N',N'-tetrabutyl-1,8-octadiamide to lithium aluminum hydride is preferably 1:3; the organic solvent is preferably tetrahydrofuran. This invention does not have specific requirements regarding the amount of the organic solvent, as long as the raw materials are fully dissolved. In this invention, the preferred method for mixing N,N,N',N'-tetrabutyl-1,8-octadiamide with lithium aluminum hydride and the organic solvent is as follows: The organic solvent and N,N,N',N'-tetrabutyl-1,8-octadiamide are added to a reaction vessel, and after bathing in an ice bath for 1 hour, lithium aluminum hydride is added.

[0058] In this invention, the temperature of the reduction reaction is preferably 60–100°C, which can be 60, 70, 80, 90, or 100°C, and the time is preferably 24–48 h, which can be 24, 36, or 48 h. In this invention, the reaction formula of the reduction reaction is shown in Formula B (where compound R2 in Formula B is N,N,N',N'-tetrabutyl-1,8-octanediamine):

[0059]

[0060] After the reduction reaction is completed, the present invention preferably cools the resulting reaction solution, then adds methanol, deionized water, and anhydrous magnesium sulfate, stirs for 1 hour, filters to obtain a clear liquid, and removes the solvent by rotary evaporation to obtain N,N,N',N'-tetrabutyl-1,8-octanediamine. In the present invention, the preferred mass ratio of methanol, deionized water, and anhydrous magnesium sulfate is 1:1:1.

[0061] After obtaining N,N,N',N'-tetrabutyl-1,8-octanediamine, the present invention mixes the N,N,N',N'-tetrabutyl-1,8-octanediamine with 1,8-dibromooctane and an organic solvent to carry out a nucleophilic substitution polymerization reaction to obtain a polycationic directed agent with the structure shown in Formula I when X is Br.

[0062] In this invention, the molar ratio of N,N,N',N'-tetrabutyl-1,8-octanediamine to 1,8-dibromooctane is preferably 1:1; the organic solvent is preferably methanol. This invention does not have specific requirements regarding the amount of organic solvent used, as long as the raw materials are fully dissolved. In the embodiments of this invention, the ratio of the total molar amount of N,N,N',N'-tetrabutyl-1,8-octanediamine and 1,8-dibromooctane to the volume of the organic solvent is 0.20 mol:100 mL. Preferably, this invention involves adding the organic solvent and N,N,N',N'-tetrabutyl-1,8-octanediamine to a reaction vessel, followed by the addition of 1,8-dibromooctane.

[0063] In this invention, the temperature of the nucleophilic substitution polymerization reaction is preferably 60–100°C, which can be 60, 70, 80, 90, or 100°C, and the time is preferably 24–96 hours, which can be 24, 36, 48, or 96 hours; the nucleophilic substitution polymerization reaction is preferably carried out under stirring and reflux conditions. In this invention, the reaction formula of the nucleophilic substitution polymerization reaction is shown in Formula C:

[0064]

[0065] After the nucleophilic substitution polymerization reaction is completed, the solvent in the resulting reaction solution is preferably removed by rotary evaporation, and then washed with n-hexane to obtain a polycationic directed agent (viscous liquid) with the structure shown in Formula I when X is Br. In this invention, the n-hexane washing is used to remove residual raw materials and solvents.

[0066] The present invention describes a polycationic directed agent with the structure shown in Formula I when X is Br, which is obtained by ion exchange with a strongly basic anion exchange resin.

[0067] In this invention, the strongly basic anion exchange resin is preferably Amberlite IRA402, a strongly basic anion exchange resin, specifically obtained by exchanging Amberlite IRA402 (chloride form) to OH form in NaOH solution, wherein the concentration of the NaOH solution is preferably 1 mol / L. In this invention, the function of the ion exchange is to replace halide anions with hydroxyl anions, obtaining a polycationic directed agent with the structure shown in Formula I when X = OH.

[0068] In this invention, the preferred specific operation of the ion exchange is as follows:

[0069] The polycationic directed agent with the structure shown in Formula I when X is Br is dissolved in water, a strong basic anion exchange resin is added to it, and the mixture is stirred and filtered in sequence, and the filtrate is collected.

[0070] The filtrate was subjected to rotary evaporation to obtain a polycationic directed agent with the structure shown in Formula I when X is OH.

[0071] In this invention, the water is preferably deionized water. When X is Br, the mass ratio of the polycationic directed agent (structure I) to water is preferably 1:2 to 10, and can be 1:5 or 1:6. When X is Br, the mass ratio of the polycationic directed agent (structure I) to the strongly basic anion exchange resin is preferably 1:1 to 5, and can be 1:2.5 or 1:3.5. In this invention, the stirring time (i.e., the ion exchange time) is preferably 8 to 24 hours, and can be 10 or 12 hours. In this invention, the filtrate is an aqueous solution of the polycationic directed agent (structure I) when X is OH. This invention does not have special requirements for the rotary evaporation conditions; simply removing the water from the filtrate is sufficient.

[0072] In this invention, since ion exchange cannot guarantee a 100% exchange rate, the obtained polycationic structure directing agent needs to be titrated with acid after rotary evaporation to determine the concentration of the OH-type polycationic structure directing agent. The OH-type polycation is then added according to the amount needed for subsequent molecular sieve synthesis. In this invention, the acid is preferably 0.1 mol / L hydrochloric acid.

[0073] In this invention, the degree of polymerization of the polycationic structure-directing agent is determined by gel permeation chromatography (GPC); the molecular weight of the polycationic structure-directing agent is determined using a WATERS 2414 differential refractive index analyzer with a WATERS ULtrahydrogel ×3 gel column; the mobile phase is 0.10M sodium nitrate aqueous solution; polyethylene glycol is used as the standard sample; and the column temperature and detector temperature are both 313K.

[0074] This invention provides a method for preparing ZSM-11 / ZSM-5 symbiotic molecular sieves, comprising the following steps:

[0075] A silicon source, an aluminum source, an alkali source, a structure-directing agent, and water are mixed and subjected to hydrothermal crystallization to obtain a crystallized product. The structure-directing agent is the polycationic structure-directing agent described in the above technical solution, and the alkali source is an alkali metal hydroxide. The silicon source is calculated as SiO2, the aluminum source as Al2O3, the alkali source as an alkali metal element, and the structure-directing agent as a structural unit. The molar ratio of the silicon source, aluminum source, structure-directing agent, alkali source, and water is 1:(0.00~0.04):(0.05~0.50):(0.02~0.50):(10~150).

[0076] The crystallized product was calcined to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve.

[0077] This invention involves mixing a silicon source, an aluminum source, an alkali source, a structure-directing agent, and water for hydrothermal crystallization to obtain a crystallized product.

[0078] In this invention, the silicon source preferably includes one or more of tetraethyl orthosilicate (TEOS), sodium silicate, fumed silica, silica sol, and silica fume; the aluminum source preferably includes one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum hydroxide, sodium aluminate, boehmite, and aluminum isopropoxide; the alkali source preferably includes one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide; and the water is preferably deionized water.

[0079] In this invention, the silicon source is calculated as SiO2, the aluminum source as Al2O3, the alkali source as an alkali metal element, and the structure-directing agent as a structural unit (i.e., [(Bu)2-C8]). The molar ratio of the silicon source, aluminum source, structure-directing agent, alkali source, and water is 1:(0~0.04):(0.05~0.50):(0.02~0.50):(10~150), or 1:(0~0.01):(0.10~0.30):(0.10~0.20):(30~60), and further, 1:(0.0025~0.01):(0.10~0.20):(0.10~0.15):(40~50). In this invention, the Si / Al ratio can be adjusted by adjusting the amount of silicon and aluminum sources, thereby achieving the adjustment of molecular sieve acidity; the higher the Si / Al ratio, the lower the acid density.

[0080] In this invention, the mixing is preferably carried out under stirring conditions. This invention does not have special requirements for the stirring conditions, as long as the components are mixed evenly. The mixing can be carried out at room temperature, that is, no additional heating or cooling is required.

[0081] In this invention, the hydrothermal crystallization temperature is preferably 110–190°C, and can be 120, 130, 140, 150, 160, 170, or 180°C; the time is preferably 3–14 days, and can be 5, 7, or 10 days. In this invention, the hydrothermal crystallization can be carried out under static or dynamic conditions, with the dynamic condition preferably being stirring, and the stirring rate being 30 rpm.

[0082] After the hydrothermal crystallization is completed, the resulting crystallization reaction solution is subjected to solid-liquid separation, solid-phase washing, and drying sequentially to obtain the crystallized product. The present invention does not have special requirements for the solid-liquid separation method; methods well-known to those skilled in the art, such as filtration or vacuum filtration, can be used. In the present invention, the washing reagent used is preferably deionized water and / or ethanol; the drying temperature is preferably 40–250°C, but can be 60, 100, or 150°C; the drying time is preferably 8–30 hours, but can be 8, 10, or 20 hours; the drying can be carried out under normal pressure or under reduced pressure.

[0083] After obtaining the crystallized product, the present invention calcines the crystallized product to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve.

[0084] In this invention, the calcination temperature is preferably 300–800°C, but can be 400, 500, 550, or 650°C, and the calcination time is preferably 1–10 hours, but can be 5, 6, or 8 hours. The calcination is preferably carried out in an oxygen-containing atmosphere, which can be air or oxygen. This invention removes the structure-directing agent through calcination to obtain ZSM-11 / ZSM-5 symbiotic molecular sieves, specifically sodium-type, potassium-type, or lithium-type ZSM-11 / ZSM-5 symbiotic molecular sieves.

[0085] After the calcination, the present invention can further subject the obtained molecular sieve to ammonium exchange (or ammonium ion exchange) and secondary calcination in sequence to obtain hydrogen-form ZSM-11 / ZSM-5 symbiotic molecular sieve.

[0086] In this invention, the ammonium exchange is preferably carried out in an ammonium salt solution, that is, the molecular sieve obtained after calcination is immersed in the ammonium salt solution. The ammonium salt in the ammonium salt solution preferably includes one or more of ammonium chloride, ammonium nitrate, ammonium carbonate, and ammonium sulfate. The concentration of ammonium ions in the ammonium salt solution is preferably 0.1-1 mol / L, which can be 0.2 or 0.5 mol / L. The solid-liquid mass ratio of the molecular sieve obtained after calcination to the ammonium salt solution is preferably 1:5-1:20, which can be 1:15 or 1:20. In this invention, the temperature of the ammonium exchange is preferably 30-80℃, which can be 55 or 65℃. The ammonium exchange is preferably carried out multiple times, with the number of ammonium exchanges preferably being 1-3 times. The time for a single ammonium exchange is preferably 1-8 hours, which can be 3 or 5 hours. After the ammonium exchange is completed, the obtained ammonium-type ZSM-11 / ZSM-5 symbiotic molecular sieve is preferably dried. The drying temperature is preferably 100℃, and the drying time is preferably 8 hours.

[0087] In this invention, the preferred temperature for the secondary calcination is 500–600°C, which can be 550°C, and the preferred time is 5–8 hours, which can be 6 hours. The secondary calcination is preferably carried out in air. After the secondary calcination, a hydrogen-form ZSM-11 / ZSM-5 symbiotic molecular sieve is obtained.

[0088] In this invention, the ZSM-11 / ZSM-5 symbiotic molecular sieve has micropores, mesopores, and macropores, with a particle size of 150–300 nm and a silicon-to-aluminum molar ratio (Si / Al) greater than or equal to 50, specifically 50–200 (i.e., a SiO2 / Al2O3 molar ratio of 100–400). In this invention, the symbiotic ratio of ZSM-11 molecular sieve to ZSM-5 molecular sieve in the ZSM-11 / ZSM-5 symbiotic molecular sieve is 80:20.

[0089] This invention provides a simple and feasible method for preparing ZSM-11 / ZSM-5 symbiotic molecular sieves. This method uses the aforementioned polycationic structure-directing agent for direct synthesis, resulting in molecular sieves with a wide silica-to-alumina ratio range (50–∞) and tunable acidity. Furthermore, the prepared ZSM-11 / ZSM-5 symbiotic molecular sieves exhibit a fixed symbiotic ratio and a hierarchical porous structure with superior diffusion performance, demonstrating excellent overall properties. A method for synthesizing hierarchical porous ZSM-11 / ZSM-5 symbiotic molecular sieves using polycationic agents has not been previously reported.

[0090] To further illustrate the present invention, the preparation methods of the polycationic structure directing agent and ZSM-11 / ZSM-5 symbiotic molecular sieve provided by the present invention are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0091] In this embodiment, the structure of the ZSM-11 / ZSM-5 symbiotic molecular sieve was determined by X-ray diffraction (XRD), which was performed using an X-ray powder diffractometer (Panalytical XPERPRO, Cu Kα ray source). The measurements were taken using a nickel filter, with a 2θ scanning range of 3–50°, an operating voltage of 40 kV, a current of 40 mA, and a scanning rate of 5° / min. Before sample testing, the crystallization of the molecular sieve samples was observed using a scanning electron microscope (SEM, model S-4800II field emission scanning electron microscope) to confirm the uniformity of the sample morphology. Based on this, XRD tests were then performed to ensure that there were no interfering peaks from other crystals in the diffraction peaks of the XRD pattern.

[0092] Example 1

[0093] Preparation of polycationic directed agents with the structure shown in Formula I (X = Br):

[0094] Add 400 mL of diethyl ether and 67.2 g (0.52 mol) of di-n-butylamine to a 1000 mL flask; after ice bath for 1 h, slowly add 25.0 g (0.13 mol) of octanyl chloride to the solution; stir the mixture at room temperature for 24 h; after the reaction is complete, filter the mixture to obtain a clear solution, wash three times with 150 mL of NaHCO3 solution (5 wt%), dry with anhydrous magnesium sulfate for 24 h, and remove the diethyl ether by rotary evaporation to obtain N,N,N',N'-tetrabutyl-1,8-octanediamide;

[0095] N,N,N',N'-Tetrabutyl-1,8-octadiamide 13 C 1 H NMR detection, results as follows Figure 1 As shown.

[0096] Add 400 mL of tetrahydrofuran and 20.0 g (0.05 mol) of N,N,N',N'-tetrabutyl-1,8-octadiamide to a 1000 mL flask. After heating in an ice bath for 1 h, add 5.7 g (0.15 mol) of lithium aluminum hydride. Then, reflux the mixture at 60 °C for 48 h. After cooling the reaction solution, slowly add 11 g of methanol, 11 g of deionized water, and 11 g of anhydrous magnesium sulfate. After stirring for 1 h, filter to obtain a clear liquid. After removing the solvent by rotary evaporation, N,N,N',N'-tetrabutyl-1,8-octadiamine is obtained.

[0097] N,N,N',N'-Tetrabutyl-1,8-octanediamine 13 C 1 H NMR detection, results as follows Figure 2 As shown.

[0098] 200 mL of methanol and 36.8 g (0.10 mol) of N,N,N',N'-tetrabutyl-1,8-octanediamine were added to a 500 mL flask, followed by 27.2 g (0.10 mol) of 1,8-dibromooctane. The mixture was stirred and refluxed at 60 °C for 96 h. The solvent was removed by rotary evaporation, and the mixture was washed with n-hexane to obtain the polycationic directed agent [-N] with the structure shown in Formula I. + (CH2CH2CH2CH3)2-(CH2)8-] n [Br - ] n (Abbreviated as [(Bu)2-C8)) n (Br)), with an average degree of polymerization of 11.

[0099] The polycationic directed agent [(Bu)2-C8] with the structure shown in Formula I (X is Br) was prepared. n (Br) proceed 13 C 1 H NMR detection, results as follows Figure 3 As shown.

[0100] Example 2

[0101] Preparation of polycationic directed agents with the structure shown in Formula I (X is OH):

[0102] 20.0 g of the polycationic structure-directing agent [(Bu)2-C8] prepared in Example 1 was used. n(Br) was dissolved in 100.0 g of deionized water, and 50 g of Amberlite IRA402 strong base anion exchange resin (obtained by exchanging Amberlite IRA402 (chloride form) to OH form in 1 mol / L NaOH solution) was added. The mixture was stirred for 12 h, filtered, and the filtrate was collected. The filtrate was rotary evaporated to remove water, and titrated with 0.1 mol / L hydrochloric acid to obtain the polycationic directed agent [-N] with the structure shown in Formula I (X is OH). + (CH2CH2CH2CH3)2-(CH2)8-] n [OH - ] n (Abbreviated as [(Bu)2-C8)) n (OH)).

[0103] Example 3

[0104] Add 8.10g of deionized water and 0.52g of [(Bu)2-C8] n (OH)(SDA, prepared in Example 2), 0.06 g sodium hydroxide, 0.01 g sodium aluminate (content 80 wt%), 2.09 g TEOS, were stirred at room temperature for 24 h to obtain a mixture. The final molar ratio of the mixture was: SiO2 / Al2O3 = 200, NaOH / SiO2 = 0.15, SDA / SiO2 = 0.20, H2O / SiO2 = 45, where SDA was calculated as structural unit (Bu)2-C8-(OH);

[0105] The mixture was placed in a stainless steel reactor and heated for 5 days under static crystallization conditions at 160°C. After crystallization, the mixture was filtered, washed, dried in an oven at 100°C for 8 hours, and calcined in air at 550°C for 6 hours to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve sample.

[0106] The X-ray diffraction pattern (XRD pattern) of the sample prepared in Example 3 is as follows: Figure 4 As shown, this is a ZSM-11 / ZSM-5 symbiotic molecular sieve, with a ZSM-11 to ZSM-5 symbiotic ratio of 80:20; the FE-SEM image of the sample is shown below. Figure 5 As shown, the particle size is between 150 and 300 nm, and the symbiotic microstructure has good uniformity.

[0107] Example 4

[0108] Add 8.10g of deionized water and 0.52g of [(Bu)2-C8] n(OH)(SDA, prepared in Example 2), 0.06 g sodium hydroxide, 2.09 g TEOS, were stirred at room temperature for 24 h to obtain a mixture. The final molar ratio of the mixture was: SiO2 / Al2O3=∞, NaOH / SiO2=0.15, SDA / SiO2=0.20, H2O / SiO2=45, where SDA was calculated as the structural unit (Bu)2-C8-(OH);

[0109] The mixture was placed in a stainless steel reactor and heated for 5 days under static crystallization conditions at 160°C. After crystallization, the mixture was filtered, washed, dried in an oven at 100°C for 8 hours, and calcined in air at 550°C for 6 hours to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve sample.

[0110] The X-ray diffraction pattern (XRD pattern) of the sample prepared in Example 4 is as follows: Figure 6 As shown, this is a pure silicon ZSM-11 / ZSM-5 symbiotic molecular sieve, with a ZSM-11 to ZSM-5 symbiotic ratio of 80:20; the FE-SEM image of the sample is shown below. Figure 7 As shown, the particle size is between 150 and 300 nm.

[0111] Example 5

[0112] Add 8.10g of deionized water and 0.52g of [(Bu)2-C8] n (OH)(SDA, prepared in Example 2), 0.04 g sodium hydroxide, 0.02 g sodium aluminate (content 80 wt%), 2.09 g TEOS, were stirred at room temperature for 24 h to obtain a mixture. The final molar ratio of the mixture was: SiO2 / Al2O3 = 100, NaOH / SiO2 = 0.10, SDA / SiO2 = 0.20, H2O / SiO2 = 45, where SDA was calculated as structural unit (Bu)2-C8-(OH);

[0113] The mixture was placed in a stainless steel reactor and heated for 5 days under static crystallization conditions at 160°C. After crystallization, the mixture was filtered, washed, dried in an oven at 100°C for 8 hours, and calcined in air at 550°C for 6 hours to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve sample.

[0114] The X-ray diffraction pattern (XRD pattern) of the sample prepared in Example 5 is as follows: Figure 8 As shown, this is a ZSM-11 / ZSM-5 symbiotic molecular sieve, with a ZSM-11 to ZSM-5 symbiotic ratio of 80:20; the FE-SEM image of the sample is shown below. Figure 9 As shown, the particle size is between 150 and 300 nm.

[0115] Example 6

[0116] Add 16.20g of deionized water and 1.03g of [(Bu)2-C8] n (OH)(SDA, prepared in Example 2), 0.12 g sodium hydroxide, 0.01 g sodium aluminate (content 80 wt%), 4.17 g TEOS, were stirred at room temperature for 24 h to obtain a mixture. The final molar ratio of the mixture was: SiO2 / Al2O3 = 400, NaOH / SiO2 = 0.15, SDA / SiO2 = 0.20, H2O / SiO2 = 45, where SDA was calculated as the structural monomer (Bu)2-C8-(OH);

[0117] The mixture was placed in a stainless steel reactor and heated for 5 days under static crystallization conditions at 160°C. After crystallization, the mixture was filtered, washed, dried in an oven at 100°C for 8 hours, and calcined in air at 550°C for 6 hours to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve sample.

[0118] The X-ray diffraction pattern (XRD pattern) of the sample prepared in Example 6 is as follows: Figure 10 As shown, this is a ZSM-11 / ZSM-5 symbiotic molecular sieve, with a ZSM-11 to ZSM-5 symbiotic ratio of 80:20; the FE-SEM image of the sample is shown below. Figure 11 As shown, the particle size is between 150 and 300 nm.

[0119] Figure 12 The N2 physical adsorption isotherm of the sample prepared in Example 6 (inset shows the pore size distribution). Figure 13 Mercury intrusion porosimetry curve of the sample prepared in Example 6 (inset shows pore size distribution, peak at 60 nm). Figures 12-13 It can be seen that, in addition to micropores, this molecular sieve also has a mesopore distribution, with pore sizes mainly concentrated in the range of 40–70 nm.

[0120] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polycationic directed agent, characterized in that, It has the structure shown in Equation I: In the structure shown in Formula I, X is Br or OH, and n is an integer from 5 to 20.

2. The method for preparing the polycationic directed agent according to claim 1, characterized in that, Includes the following steps: A nucleophilic addition reaction was carried out by mixing di-n-butylamine, octanoyl chloride and an organic solvent to give N,N,N',N'-tetrabutyl-1,8-octanoyldiamide; The N,N,N',N'-tetrabutyl-1,8-octadiamide was mixed with lithium aluminum hydride and an organic solvent for a reduction reaction to obtain N,N,N',N'-tetrabutyl-1,8-octadiamine; The N,N,N',N'-tetrabutyl-1,8-octanediamine was mixed with 1,8-dibromooctane and an organic solvent to carry out a nucleophilic substitution polymerization reaction to obtain a polycationic directed agent with the structure shown in Formula I when X is Br. When X is Br, the polycationic directed agent of Formula I is subjected to ion exchange through a strongly basic anion exchange resin to obtain the polycationic directed agent of Formula I when X is OH.

3. The preparation method according to claim 2, characterized in that, The molar ratio of di-n-butylamine to octanoyl chloride is 4:1, and the nucleophilic addition reaction is carried out at room temperature for 24–48 hours.

4. The preparation method according to claim 2, characterized in that, The molar ratio of N,N,N',N'-tetrabutyl-1,8-octadiamide to lithium aluminum hydride is 1:3, and the reduction reaction is carried out at a temperature of 60–100 °C for 24–48 h.

5. The preparation method according to claim 2, characterized in that, The molar ratio of N,N,N',N'-tetrabutyl-1,8-octanediamine to 1,8-dibromooctane is 1:1, and the nucleophilic substitution polymerization reaction is carried out at a temperature of 60–100 °C for a time of 24–96 h.

6. A method for preparing ZSM-11 / ZSM-5 symbiotic molecular sieves, characterized in that, Includes the following steps: A structure-directing agent, a silicon source, an aluminum source, an alkali source, and water are mixed and subjected to hydrothermal crystallization to obtain a crystallized product; the structure-directing agent is the polycationic structure-directing agent according to claim 1, and the alkali source is an alkali metal hydroxide; the silicon source is calculated as SiO2, the aluminum source as Al2O3, the alkali source as an alkali metal element, and the structure-directing agent as a structural unit; the molar ratio of the silicon source, aluminum source, structure-directing agent, alkali source, and water is 1:(0~0.04):(0.05~0.50):(0.02~0.50):(10~150); The crystallized product was calcined to obtain the ZSM-11 / ZSM-5 symbiotic molecular sieve.

7. The preparation method according to claim 6, characterized in that, The silicon source includes one or more of tetraethyl orthosilicate, sodium silicate, fumed silica, silica sol, and silica fume; the aluminum source includes one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum hydroxide, sodium aluminate, boehmite, and aluminum isopropoxide; and the alkali source includes one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

8. The preparation method according to claim 6, characterized in that, The hydrothermal crystallization temperature is 110–190°C, and the time is 3–14 days.

9. The preparation method according to claim 6, characterized in that, The ZSM-11 / ZSM-5 symbiotic molecular sieve has micropores and mesopores, with a particle size of 150-300 nm and a silicon-aluminum molar ratio greater than or equal to 50.

10. The preparation method according to claim 6 or 9, characterized in that, The symbiotic ratio of ZSM-11 molecular sieve to ZSM-5 molecular sieve in the ZSM-11 / ZSM-5 symbiotic molecular sieve is 80:20.

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