Method for preparing MCM-36 molecular sieve under mild condition
阅读说明：本技术 一种温和条件下制备mcm-36分子筛的方法 (Method for preparing MCM-36 molecular sieve under mild condition ) 是由 张智芳 冯利军 冯亚军 于 2020-11-11 设计创作，主要内容包括：本发明公开了一种温和条件下制备MCM-36分子筛的方法,该方法以MCM-22(P)为前驱体,采用不同结构和亲水性能的Gemini季铵盐类阳离子表面活性剂作为层间结构导向剂,以正硅酸乙酯(TEOS)为氧化物“柱”前驱体,合成了层柱结构MCM-36分子筛。本发明所采用的Gemini季铵盐类阳离子表面活性剂具有较强的亲水性,可以保留MWW片层之间更多的水分,从而使TEOS可以在弱碱性条件下利用层间水分在层间限域空间内水解聚合形成氧化硅“柱”,获得结构更加规整、孔径分布集中的分子筛MCM-36,而且本制备方法简单,省去了传统方法中水解的步骤。(The invention discloses a method for preparing an MCM-36 molecular sieve under mild conditions, which synthesizes the MCM-36 molecular sieve with a layer-column structure by taking MCM-22(P) as a precursor, adopting Gemini quaternary ammonium salt cationic surfactants with different structures and hydrophilicity as an interlayer structure directing agent and Tetraethoxysilane (TEOS) as an oxide column precursor. The Gemini quaternary ammonium salt cationic surfactant adopted by the invention has stronger hydrophilicity and can retain more water between MWW sheets, so that TEOS can form a silicon oxide column by utilizing the hydrolysis polymerization of interlayer water in an interlayer confinement space under the alkalescent condition, the molecular sieve MCM-36 with more regular structure and concentrated pore size distribution is obtained, and the preparation method is simple and omits the hydrolysis step in the traditional method.)
1. A method for preparing MCM-36 molecular sieve under mild condition is characterized by comprising the following steps:
(1) preparation of layered MCM-22(P)
According to the molar ratio: SiO 22/Al2O3＝30～100、OH–/SiO2＝0.14～0.3、HMI/SiO2＝0.3～0.7、H2O/SiO240-45, wherein HMI represents hexamethyleneimine, sodium hydroxide is completely dissolved in deionized water at room temperature, sodium metaaluminate is continuously added under stirring, silica sol is gradually added after the sodium metaaluminate is completely dissolved, the stirring is continuously carried out for 20-40 minutes, HMI is added, the uniform stirring is carried out, the obtained mixed solution is placed in a stainless steel reaction kettle with a polytetrafluoroethylene lining, and the stirring and crystallization are carried out at 140-160 ℃ under the closed condition; after the reaction is finished, taking out the stainless steel reaction kettle, placing the stainless steel reaction kettle in cold water for quenching, centrifugally washing the reaction liquid until the supernatant is neutral, and drying the lower-layer precipitate at the temperature of 60-80 ℃ to obtain layered MCM-22 (P);
(2) intercalation swelling of MCM-22(P)
The weight ratio is as follows: h240-50% of O/MCM-22(P), 10-20% of TPAOH/MCM-22(P) and 8-12% of Gemini/MCM-22(P), wherein TPOAC represents dimethyl octadecyl [3- (trimethoxysilyl) propyl group]Grinding the layered MCM-22(P) obtained in the step (1) into powder, stirring and dispersing the powder in deionized water, ultrasonically dispersing TPAOH and Gemini quaternary ammonium salt cationic surfactants in the deionized water, uniformly mixing the two aqueous solutions, regulating the pH value to be 8-9 by using the TPAOH, stirring for 15-20 hours at 30-40 ℃, centrifugally washing, and drying at 30-40 ℃ to obtain the swollen MCM-22 (P);
the structural formula of the Gemini quaternary ammonium salt cationic surfactant is shown as follows:
wherein R represents a linear alkyl group;
(3) MCM-22(P) column support
The weight ratio is as follows: mixing the swelled MCM-22(P) and TEOS, stirring for 5-8 hours at 30-40 ℃, centrifugally washing, and drying at 30-40 ℃ to obtain MCM-36 (P); heating MCM-36(P) to 450-600 ℃ at the heating rate of 2-5 ℃/min in the air atmosphere, and roasting at the constant temperature for 5-8 hours to obtain the MCM-36 molecular sieve.
2. A process for the preparation of MCM-36 molecular sieves under mild conditions as claimed in claim 1, characterized in that: in the step (1), the molar ratio is as follows: SiO 22/Al2O3＝50、OH–/SiO2＝0.14、HMI/SiO2＝0.35、H2O/SiO2＝45。
3. A process for the preparation of MCM-36 molecular sieves under mild conditions according to claim 1 or claim, characterized in that: in the step (2), the mixture is stirred and crystallized for 7 days at 150 ℃ under a closed condition.
4. A process for the preparation of MCM-36 molecular sieves under mild conditions as claimed in claim 1, characterized in that: in the step (2), R represents C7、C11Or C15Saturated straight-chain alkyl groups of (1).
5. A process for the preparation of MCM-36 molecular sieves under mild conditions as claimed in claim 1, characterized in that: in the step (3), the MCM-36(P) is heated to 550 ℃ at the heating rate of 2-3 ℃/min in the air atmosphere, and is roasted for 6 hours at the constant temperature.
Technical Field
The invention belongs to the technical field of molecular sieves and porous materials, and particularly relates to a method for preparing an MCM-36 molecular sieve under mild conditions.
Background
MCM-36 molecular sieve is MWW type molecular sieve with pillared structure, and is generally prepared by swelling MCM-22 precursor and using SiO2、Al2O3And MgO and the like. Compared with MCM-22 precursor, the MCM-36 molecular sieve reserves original ten-membered ring sinusoidal channels and ten-membered ring sinusoidal channelsIn addition, due to the fact that a mesoporous hole with the diameter of about 3-3.5 nm is formed on the outer surface of the two-membered ring through the pillared support, the BET specific surface area of the mesoporous structure is 2.5-3 times of that of the MCM-22 molecular sieve, and the introduction of the mesoporous structure can effectively improve the catalytic performance of reactions in which macromolecules participate and are generated. In short, because the unique pore channel structure in the MCM-36 molecular sieve can expose the pores on the outer surface thereof to the greatest extent, and the main active centers catalyzing larger molecular reactions are considered to be acid sites distributed in the pores on the outer surface of the molecular sieve after being researched, the MCM-36 molecular sieve with a larger specific surface area has been widely noticed, and shows catalytic performance different from the normal catalytic performance in catalytic reactions such as isobutane-butene alkylation, xylene disproportionation, methane oxygen-free aromatization, catalytic cracking of gasoline and the like.
Maheshwari (Journal of the American Chemical Society,2008,130(4):1507-1516) and the like investigated the swelling of MCM-22 precursors with cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) as swelling agents at room temperature and high pH (pH 13.8) and then converted to MCM-36 molecular sieves with ordered layered structures by column support. However, since silica has high solubility in highly alkaline aqueous solutions during the pillaring process, the structural integrity is still destroyed and the acidity of the molecular sieve is reduced. Roth (Catalysis Today,2013,204(204):8-14) and the like explored that at room temperature, an MCM-22 precursor is swelled by using CTMA-Cl and 25% tetramethylammonium hydroxide (TMA-OH) as swelling agents, then Tetraethoxysilane (TEOS) is used for stirring at the high temperature of 95 ℃ overnight, and deionized water is used for stirring overnight to obtain a pillared MCM-36 molecular sieve, the influence of different amounts of TMA-OH and surfactants on the swelling degree is firstly measured by X-ray diffraction, and the size effect of cations in the swelling process is denied.
Disclosure of Invention
The invention aims to provide a method for preparing an MCM-36 molecular sieve under mild conditions, and a step of further adding water for hydrolysis in the traditional method is omitted.
Aiming at the purposes, the technical scheme adopted by the invention comprises the following steps:
1. preparation of layered MCM-22(P)
According to the molar ratio: SiO 22/Al2O3＝30～100、OH–/SiO2＝0.14～0.3、HMI/SiO2＝0.3～0.7、H2O/SiO240-45, wherein HMI represents hexamethyleneimine, sodium hydroxide is completely dissolved in deionized water at room temperature, sodium metaaluminate is continuously added under stirring, silica sol is gradually added after the sodium metaaluminate is completely dissolved, the stirring is continuously carried out for 20-40 minutes, HMI is added, the uniform stirring is carried out, the obtained mixed solution is placed in a stainless steel reaction kettle with a polytetrafluoroethylene lining, and the stirring and crystallization are carried out at 140-160 ℃ under the closed condition; and after the reaction is finished, taking out the stainless steel reaction kettle, placing the stainless steel reaction kettle in cold water for quenching, centrifugally washing the reaction liquid until the supernatant is neutral, and drying the lower-layer precipitate at the temperature of 60-80 ℃ to obtain the layered MCM-22 (P).
2. Intercalation swelling of MCM-22(P)
The weight ratio is as follows: h240-50% of O/MCM-22(P), 10-20% of TPAOH/MCM-22(P) and 8-12% of Gemini/MCM-22(P), wherein TPOAC represents dimethyl octadecyl [3- (trimethoxysilyl) propyl group]And (2) grinding the layered MCM-22(P) obtained in the step (1) into powder, stirring and dispersing the powder in deionized water, ultrasonically dispersing TPAOH and Gemini quaternary ammonium salt cationic surfactant in the deionized water, uniformly mixing the two aqueous solutions, adjusting the pH to 8-9 by using the TPAOH, stirring for 15-20 hours at 30-40 ℃, centrifugally washing, and drying at 30-40 ℃ to obtain the swollen MCM-22 (P).
3. MCM-22(P) column support
The weight ratio is as follows: mixing the swelled MCM-22(P) and TEOS, stirring for 5-8 hours at 30-40 ℃, centrifugally washing, and drying at 30-40 ℃ to obtain MCM-36 (P); heating MCM-36(P) to 450-600 ℃ at the heating rate of 2-5 ℃/min in the air atmosphere, and roasting at the constant temperature for 5-8 hours to obtain the MCM-36 molecular sieve.
In the step 1, it is preferable that the molar ratio is: SiO 22/Al2O3＝50、OH–/SiO2＝0.14、HMI/SiO2＝0.35、H2O/SiO2＝45。
In the step 2, the structural formula of the Gemini quaternary ammonium salt cationic surfactant is as follows:
wherein R represents a straight-chain alkyl group, preferably R represents C7、C11Or C15Saturated straight-chain alkyl groups of (1). The Gemini quaternary ammonium salt cationic surfactant is prepared according to the method disclosed in the publication No. CN104525044A and the invention name of Gemini quaternary ammonium salt cationic surfactant and the synthesis method thereof.
In the step 2, it is more preferable to crystallize the crystals under stirring at 150 ℃ for 7 days under a sealed condition.
In the step 3, preferably, MCM-36(P) is heated to 550 ℃ at the heating rate of 2-3 ℃/min in the air atmosphere, and is roasted for 6 hours at the constant temperature.
The invention has the following beneficial effects:
the invention takes HMI as organic template agent, SiO2The sol is silicon source, NaAlO2The Gemini quaternary ammonium salt cationic surfactant with different structures and hydrophilic properties is used as an interlayer structure directing agent as an aluminum source, so that a strong acting force caused by hydrogen bonds in MCM-22(P) is effectively eliminated, efficient swelling of the MCM-22(P) is realized under mild conditions (T is 30-40 ℃, and pH is 7.5-8.5), and TEOS (SiO) is directed2Precursor of (a) are assembled among MWW sheets, thereby obtaining the MCM-36 molecular sieve with different interlayer pore structures and pore diameters. In the column supporting process, the step of hydrolysis in the traditional method is omitted, and the MCM-36 molecular sieve with high external specific surface area, which is formed by orderly arranging MWW lamella basic units and interlayer oxide columns, is obtained by column supporting under mild conditions.
Drawings
FIG. 1 is a small angle XRD pattern of the MCM-36 molecular sieve prepared in example 1.
FIG. 2 is a wide angle XRD pattern of the MCM-36 molecular sieve prepared in example 1.
FIG. 3 is an SEM photograph of the MCM-36 molecular sieve prepared in example 1.
Detailed Description
The invention will be further described in detail with reference to the following figures and examples, but the scope of the invention is not limited to these examples.
Example 1
1. Preparation of layered MCM-22(P)
According to the molar ratio: SiO 22/Al2O3＝50、OH–/SiO2＝0.14、HMI/SiO2＝0.35、H2O/SiO245 g NaOH was dissolved in 50.32g deionized water at room temperature, and then 0.30g NaAlO was added with stirring2After complete dissolution, 9.34g of SiO were added dropwise2The sol was further stirred for 30mins, 2.18g HMI was added dropwise, the resulting mixture was transferred to a stainless steel reactor with a 100mL Teflon liner, placed in a homogeneous reactor and reacted for 7 days at 150 ℃ with stirring at 60 r/min. After the reaction is finished, a stainless steel reaction kettle is unloaded from the homogeneous reactor and is placed into flowing cold water for cooling, the mixture is separated by a centrifuge, deionized water is repeatedly washed until the pH value is about 7, and the mixture is dried in a drying oven at 60 ℃ for 12 hours to obtain the layered MCM-22.
2. Intercalation swelling of MCM-22(P)
The weight ratio is as follows: h2Adding 1g of lamellar MCM-22(P) which is ground into powder and 20g of deionized water into a 150mL flask, and magnetically stirring the mixture, wherein O/MCM-22(P) is 50, TPAOH/MCM-22(P) is 20, and Gemini/MCM-22(P) is 10; 20g of TPAOH, 30g H2Adding O and 10g of Gemini quaternary ammonium salt cationic surfactant into a beaker, performing ultrasonic treatment for 30 minutes, pouring the mixture into the flask, stirring for 5 minutes, controlling the pH value of the mixed solution in the flask to be 8-9 by adding TPAOH, performing oil bath stirring for 16 hours at 35 ℃, performing centrifugal washing by using ethanol and deionized water in sequence, and finally drying in a drying oven at 35 ℃ to obtain the swollen MCM-22 (P).
The structural formula of the cationic surfactant of Gemini quaternary ammonium salt in the embodiment is as follows:
3. MCM-22(P) column support
The weight ratio is as follows: swollen MCM-22(P)/TEOS ═ 10, mixing 1g swollen MCM-22(P) with 10g TEOS, stirring at 35 ℃ for 5h, washing by centrifugation, drying at 35 ℃ to give MCM-36 (P); heating MCM-36(P) to 550 ℃ at the heating rate of 2 ℃/min in the air atmosphere of a muffle furnace, and roasting at constant temperature for 6 hours to obtain the MCM-36 molecular sieve.
The characterization was carried out using an X-ray diffractometer (model D8 Advance, Bruker, Germany) MCM-36 molecular sieve, and the results are shown in FIGS. 1 and 2. As can be seen from fig. 1, the crystallinity of the molecular sieve is good, and a 001 characteristic diffraction peak representing the interlayer spacing appears between 2 θ and 1.5 ° to 2 ° in the swelled and pillared MCM-36, which indicates that the three molecular sieves successfully form an interlayer mesoporous structure and contain new unit cell c-axis parameters. And d of CTAB-MCM-36 can be obtained by calculation001D value of 4.2nm, CPAB-MCM-36001A value of 4.4nm, a Gemini-MCM-36 d001A value of 4.7nm, corresponding to conventional d001Compared with MCM-22 with the value of only 2.7nm, the value is obviously increased. As can be seen from the XRD pattern in FIG. 2, in a large angle range, the three MCM-36 patterns are similar to those of MCM-22, and MWW structure characteristic diffraction peaks appear, which indicates that the original structural unit layer of the MCM-22 molecular sieve is not damaged by swelling, pillaring and high-temperature roasting processes at room temperature. In addition, the peaks of 101 and 102 characteristic diffraction peaks of the MCM-36 molecular sieve between 2 theta and 5-10 degrees tend to be broadened, which shows that the c axis of the unit cell may be inhomogeneous due to the pillaring process.
Example 2
1. Preparation of layered MCM-22(P)
This step is the same as step 1 of example 1.
2. Intercalation swelling of MCM-22(P)
The weight ratio is as follows: h2Adding 1g of lamellar MCM-22(P) which is ground into powder and 20g of deionized water into a 150mL flask, and magnetically stirring the mixture; 10g of the powderTPAOH、20g H2Adding O and 8g of Gemini quaternary ammonium salt cationic surfactant into a beaker, performing ultrasonic treatment for 30 minutes, pouring the mixture into the flask, stirring for 5 minutes, controlling the pH value of the mixed solution in the flask to be 8-9 by adding TPAOH, performing oil bath stirring for 16 hours at 35 ℃, performing centrifugal washing by using ethanol and deionized water in sequence, and finally drying in a drying oven at 35 ℃ to obtain the swollen MCM-22 (P).
The structural formula of the cationic surfactant of Gemini quaternary ammonium salt in the embodiment is as follows:
3. MCM-22(P) column support
The weight ratio is as follows: swollen MCM-22(P)/TEOS 15, mixing 1g of swollen MCM-22(P) with 15g of TEOS, stirring at 35 ℃ for 5h, washing by centrifugation, and drying at 35 ℃ to obtain MCM-36 (P); heating MCM-36(P) to 550 ℃ at the heating rate of 2 ℃/min in the air atmosphere of a muffle furnace, and roasting at constant temperature for 6 hours to obtain the MCM-36 molecular sieve.
Example 3
1. Preparation of layered MCM-22(P)
This step is the same as step 1 of example 1.
2. Intercalation swelling of MCM-22(P)
The weight ratio is as follows: h2Adding 1g of lamellar MCM-22(P) which is ground into powder and 25g of deionized water into a 150mL flask, and magnetically stirring the mixture, wherein O/MCM-22(P) is 45, TPAOH/MCM-22(P) is 20, and Gemini/MCM-22(P) is 12; 20g of TPAOH, 20g H2Adding O and 12g of Gemini quaternary ammonium salt cationic surfactant into a beaker, performing ultrasonic treatment for 30 minutes, pouring the mixture into the flask, stirring for 5 minutes, controlling the pH value of the mixed solution in the flask to be 8-9 by adding TPAOH, performing oil bath stirring for 16 hours at 35 ℃, performing centrifugal washing by using ethanol and deionized water in sequence, and finally drying in a drying oven at 35 ℃ to obtain the swollen MCM-22 (P).
The structural formula of the cationic surfactant of Gemini quaternary ammonium salt in the embodiment is as follows:
3. MCM-22(P) column support
The weight ratio is as follows: swollen MCM-22(P)/TEOS ═ 20, 1g swollen MCM-22(P) was mixed with 20g TEOS, stirred at 35 ℃ for 5h, washed by centrifugation, dried at 35 ℃ to give MCM-36 (P); heating MCM-36(P) to 550 ℃ at the heating rate of 2 ℃/min in the air atmosphere of a muffle furnace, and roasting at constant temperature for 6 hours to obtain the MCM-36 molecular sieve.
Example 4
In the intercalation swelling step 2 of MCM-22(P), oil bath stirring is carried out for 20 hours at the temperature of 30 ℃, ethanol and deionized water are sequentially used for centrifugal washing, and finally drying is carried out in a drying oven at the temperature of 30 ℃; in the step 3 of supporting MCM-22(P), stirring is carried out for 8h at 30 ℃, centrifugal washing is carried out, and drying is carried out at 30 ℃. The other steps are the same as the example 1, and the MCM-36 molecular sieve is obtained.
Example 5
In the intercalation swelling step 2 of MCM-22(P), oil bath stirring is carried out for 15h at the temperature of 40 ℃, ethanol and deionized water are sequentially used for centrifugal washing, and finally drying is carried out in a drying oven at the temperature of 40 ℃; in the step 3 of supporting MCM-22(P), the mixture is stirred for 5 hours at 40 ℃, centrifugally washed and dried at 40 ℃. The other steps are the same as the example 1, and the MCM-36 molecular sieve is obtained.
Example 6
In the step 3 of supporting MCM-22(P), the temperature is raised to 450 ℃ at the heating rate of 3 ℃/min in a muffle furnace under the air atmosphere, and the mixture is roasted for 8 hours at constant temperature; the other steps are the same as the example 1, and the MCM-36 molecular sieve is obtained.
Example 7
In the step 3 of supporting MCM-22(P), the temperature is raised to 600 ℃ at the heating rate of 3 ℃/min in a muffle furnace under the air atmosphere, and the mixture is roasted for 5 hours at constant temperature; the other steps are the same as the example 1, and the MCM-36 molecular sieve is obtained.