A method for preparing strongly adsorbed MCM-41 molecular sieve

Abstract

The invention belongs to the field of molecular sieve preparation, and specifically relates to a method for preparing a strongly adsorbed MCM-41 molecular sieve. The invention uses vinyl trimethoxysilane and ethylene glycol dimethacrylate as hydrophobic modifiers, and pre-freezes the molecular sieve, and utilizes the temperature difference between the molecular sieve raw material and the hydrophobic modifier to effectively promote the hydrophobic modifier to enter the molecular sieve pores. In addition, after the polymerization reaction is completed, the molecular sieve is washed with ethanol, which can destroy the hydrogen bonding between hydroxyl groups inside the molecular sieve and play the role of a pore expander on the one hand, and can remove the blockage of the molecular sieve pores by polymers formed by self-polymerization of vinyl trimethoxysilane and ethylene glycol dimethacrylate on the other hand, thereby improving the strength and adsorption performance of the molecular sieve.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and in particular relates to a method for preparing a strong adsorption MCM-41 molecular sieve. Background Art

[0002] Molecular sieves are a type of inorganic porous crystalline material with three-dimensional four-connected and regular pore structures formed by peroxide bridges. Due to its high specific surface area, good thermal stability and strong surface acidity, it exhibits excellent catalytic, ion exchange, adsorption and separation properties, and is mostly used in important fields such as petroleum catalytic cracking, fine chemicals, environmental chemicals, and daily chemicals. MCM-41 is a pure silicon mesoporous molecular sieve with hexagonal orderly pores and extremely high order. This regular structure provides a good foundation for its application in catalysis, adsorption, separation and other fields, making the transmission and interaction of molecules in the pores highly directional and selective. Uniform and adjustable pore size: The pore size is uniform and can be continuously adjusted in the range of 2-10nm, which can meet the needs of processing or separating substances of different molecular sizes. It is also widely concerned in VOCs research. In order to further improve the selective adsorption performance of molecular sieves, ion exchange, chemical deposition, heat treatment, amine modification, acid-base treatment and other methods have been tried to modify its pore structure and surface properties in order to obtain ideal adsorption performance.

[0003] Prior art CN 115445582 B discloses a hydrophobically modified molecular sieve and its preparation method and application. First, the molecular sieve is surface-modified and pretreated by vinyl trimethoxysilane to provide a vinyl group with high activity on the surface of the molecular sieve, enhance the interaction between divinylbenzene and the molecular sieve during the polymerization process, reduce the defects between the finally synthesized polydivinylbenzene and the molecular sieve, and the surface of the obtained hydrophobically modified molecular sieve contains highly cross-linked polydivinylbenzene that can provide hydrophobic effect, and has a large specific surface area and excellent pore structure. Prior art CN112390270A discloses a hydrophobically modified ZSM-5 molecular sieve and its preparation method and application, and the preparation method of the hydrophobically modified ZSM-5 molecular sieve comprises the following steps: 1) calcining and activating the ZSM-5 molecular sieve to obtain an activated ZSM-5 molecular sieve; 2) adding the activated ZSM-5 molecular sieve to ethanol, then adding vinyl trimethoxysilane, and performing a reflux reaction to obtain a hydrophobically modified ZSM-5 molecular sieve. The invention uses ethanol as a reaction solvent, and can hydrophobically modify the ZSM-5 molecular sieve under low temperature conditions. The method is simple, easy, safe and environmentally friendly. The obtained hydrophobically modified ZSM-5 molecular sieve has high crystallinity, large pore volume, large specific surface area, excellent hydrophobic performance, and strong adsorption capacity for organic matter under high humidity environment. Although the modification method mentioned in the above-mentioned related prior art can access more organic functional groups, the distribution of functional groups on the surface of the modified material prepared by this method is very uneven, most of which are concentrated in the area near the orifice of the outer surface and inner surface of the pore, and the content of functional groups distributed inside the pore is less, resulting in limited improvement in its adsorption capacity. Therefore, it is necessary to provide a method for preparing a high-intensity and strongly adsorbed zeolite molecular sieve to overcome the above-mentioned technical problems. Summary of the invention

[0004] Based on the technical problems mentioned in the above background technology, the present invention uses vinyltrimethoxysilane and ethylene glycol dimethacrylate as hydrophobic modifiers, and pre-freezes the molecular sieve, and utilizes the temperature difference between the molecular sieve raw material and the hydrophobic modifier to effectively promote the hydrophobic modifier to enter the interior of the molecular sieve pores, thereby improving the adsorption capacity of the molecular sieve through the modification treatment.

[0005] An object of the present invention is to provide a method for preparing a strongly adsorbing MCM-41 molecular sieve, which is characterized by comprising the following steps:

[0006] S1: Freeze the molecular sieve at -30℃ to -20℃ for 4-8h, take vinyltrimethoxysilane and place it in a constant temperature shaker, keep it warm at 25℃ for 20-30min, then add the frozen molecular sieve to the vinyltrimethoxysilane solution, stir for 4-12h, and then freeze-dry at -20℃ for 6h to obtain the primary modified molecular sieve.

[0007] S2: Ethylene glycol dimethacrylate and azobisisoheptylnitrile are uniformly mixed to obtain an ethylene glycol dimethacrylate solution, wherein the mass ratio of ethylene glycol dimethacrylate to azobisisoheptylnitrile is 1:0.001-0.005.

[0008] S3: Add the primary modified molecular sieve obtained in step S1 to the ethylene glycol dimethacrylate solution in step S2, stir at room temperature for 2-4 hours, increase the temperature to 50-53°C at a certain heating rate, and maintain for 8-12 hours. After the polymerization is completed, wash with ethanol for 6-8 times and dry.

[0009] Furthermore, the MCM-41 in step S1 is a mesoporous molecular sieve.

[0010] Furthermore, in step S1, the volume ratio of vinyltrimethoxysilane to molecular sieve is 0.8-1:1.

[0011] Furthermore, in step S1, the freezing temperature of the molecular sieve is -20°C, and the freezing time is 6 hours.

[0012] Before the molecular sieve is modified by vinyltrimethoxysilane, the molecular sieve is subjected to freezing pretreatment. On the one hand, during the contact process between the molecular sieve and the modifier, the molecular sieve at a relatively low temperature contacts the modifier at a relatively high temperature. Due to the temperature difference between the molecular sieve and the modifier, the low-temperature molecular sieve absorbs the heat of the modifier, cools and shrinks the modifier, and helps to infiltrate the modifier into the interior of the molecular sieve, thereby increasing the access amount of the hydrophobic modifier. On the other hand, the modification of the molecular sieve by vinyltrimethoxysilane is a process in which the hydrolysis product of vinyltrimethoxysilane forms a covalent bond with the silanol group on the surface of the molecular sieve. The molecular sieve is subjected to pre-freezing treatment by the present invention, which can timely transfer the heat generated in the process of forming the covalent bond, and can effectively promote the modification process of the molecular sieve by vinyltrimethoxysilane.

[0013] Furthermore, in step S2, the mass ratio of ethylene glycol dimethacrylate to azobisisoheptanenitrile is 1:0.005.

[0014] In the present invention, azobisisoheptanenitrile is used as a polymerization initiator, which can initiate free radical polymerization between ethylene glycol dimethacrylate and vinyltrimethoxysilane at a relatively low temperature, and cooperate with the polymerization temperature set in the present invention to help form more short-chain polymers, thereby avoiding blocking the molecular sieve pores and affecting its adsorption performance.

[0015] Furthermore, in step S3, the volume ratio of ethylene glycol dimethacrylate to the primary modified molecular sieve is 2-4:1.

[0016] Furthermore, the volume concentration of ethanol in step S3 is 50%-75%.

[0017] In the present invention, ethanol is used to wash the molecular sieve after polymerization, which can remove the blockage of the molecular sieve pores by the polymer formed by the self-polymerization of vinyltrimethoxysilane and ethylene glycol dimethacrylate, thereby avoiding affecting the pore structure and adsorption performance of the molecular sieve.

[0018] Furthermore, the heating rate in step S3 is 10-15°C / min.

[0019] Furthermore, the heating rate in step S3 is 12° C. / min.

[0020] Furthermore, in step S3, the temperature is raised to 52° C. and maintained for 10 hours.

[0021] In the present application, the polymerization is carried out at a lower temperature, the activity of the initiator is reduced, and it is helpful to produce a polymer with a lower molecular weight. At a higher temperature, the activity of the initiator increases, the molecular kinetic energy increases, and the collision frequency between molecules increases, thereby increasing the rate of free radical generation and the growth rate of the polymer chain, resulting in the production of a polymer with a higher molecular weight, which blocks the molecular sieve pores.

[0022] The present invention has the following beneficial effects:

[0023] The present invention uses vinyltrimethoxysilane to pretreat the molecular sieve before using ethylene glycol dimethacrylate for modification, which can improve the reaction activity of the molecular sieve and is beneficial to enhancing the interaction between the ethylene glycol dimethacrylate and the molecular sieve during the polymerization process.

[0024] Before the molecular sieve is modified by using ethylene glycol dimethacrylate and vinyl trimethoxysilane, the molecular sieve is subjected to freezing pretreatment. After the molecular sieve is subjected to freezing pretreatment, the molecular sieve at a relatively low temperature contacts the modifying agent at a relatively high temperature during the contact process between the molecular sieve and the modifying agent. Due to the temperature difference between the molecular sieve and the modifying agent, the low-temperature molecular sieve absorbs the heat of the modifying agent, cools down and shrinks the modifying agent, and helps the modifying agent to penetrate into the interior of the molecular sieve, thereby increasing the access amount of the hydrophobic modifying agent.

[0025] The present invention adopts ethylene glycol dimethacrylate as a hydrophobic modifier, and a dipole effect can be formed between the ester group in the molecular structure and the hydroxyl group in the molecular sieve, which helps the ethylene glycol dimethacrylate to enter the pores of the molecular sieve and increase the grafting amount.

[0026] After the polymerization of vinyltrimethoxysilane and ethylene glycol dimethacrylate is completed, ethanol is used to wash the molecular sieve. On the one hand, ethanol can destroy the hydrogen bonding between the hydroxyl groups inside the molecular sieve and play the role of a pore expander. On the other hand, ethanol can remove the blockage of the molecular sieve pores by the polymer formed by the self-polymerization of vinyltrimethoxysilane and ethylene glycol dimethacrylate. DETAILED DESCRIPTION

[0027] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. The present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and the concept of the present invention will be fully conveyed to those skilled in the art, and the present invention will only be limited by the claims.

[0028] Example 1

[0029] The mesoporous MCM-41 molecular sieve raw material was frozen at -30°C for 4 hours, and vinyltrimethoxysilane with a volume ratio of 0.8:1 to the molecular sieve was placed in a constant temperature shaker, kept warm at 25°C for 30 minutes, and then the frozen molecular sieve was added to the vinyltrimethoxysilane solution, stirred at a constant temperature for 4 hours, and then freeze-dried at -20°C for 6 hours to obtain a primary modified molecular sieve, and ethylene dimethacrylate was taken according to a volume ratio of primary modified molecular sieve: ethylene glycol dimethacrylate of 1:2, and azobisisoheptanenitrile was added according to a mass ratio of ethylene glycol dimethacrylate: azobisisoheptanenitrile of 1:0.001. After stirring evenly, the primary modified molecular sieve was added to the ethylene glycol dimethacrylate solution, stirred at room temperature for 2 hours, and then the temperature was increased to 50°C at a heating rate of 10°C / min and maintained for 8 hours. After the polymerization was completed, it was washed 6-8 times with 75% ethanol and dried to obtain the molecular sieve.

[0030] Example 2

[0031] The mesoporous MCM-41 molecular sieve raw material was frozen at -20°C for 6 hours, and vinyltrimethoxysilane with a volume ratio of 1:1 to the molecular sieve was placed in a constant temperature shaker, kept warm at 25°C for 25 minutes, and then the frozen molecular sieve was added to the vinyltrimethoxysilane solution, stirred at a constant temperature for 4 hours, and then freeze-dried at -20°C for 6 hours to obtain a primary modified molecular sieve, and ethylene dimethacrylate was taken according to a volume ratio of primary modified molecular sieve: ethylene glycol dimethacrylate of 1:3, and azobisisoheptanenitrile was added according to a mass ratio of ethylene glycol dimethacrylate: azobisisoheptanenitrile of 1:0.005. After stirring evenly, the primary modified molecular sieve was added to the ethylene glycol dimethacrylate solution, stirred at room temperature for 3 hours, and then the temperature was increased to 52°C at a heating rate of 12°C / min and maintained for 10 hours. After the polymerization was completed, it was washed 6-8 times with 60% ethanol and dried to obtain the molecular sieve.

[0032] Example 3

[0033] The mesoporous MCM-41 molecular sieve raw material was frozen at -25°C for 8 hours, and vinyltrimethoxysilane with a volume ratio of 0.8:1 to the molecular sieve was placed in a constant temperature shaker, kept warm at 25°C for 30 minutes, and then the frozen molecular sieve was added to the vinyltrimethoxysilane solution, stirred at a constant temperature for 4 hours, and then freeze-dried at -20°C for 6 hours to obtain a primary modified molecular sieve, and ethylene dimethacrylate was taken according to a volume ratio of primary modified molecular sieve: ethylene glycol dimethacrylate of 1:4, and azobisisoheptanenitrile was added according to a mass ratio of ethylene glycol dimethacrylate: azobisisoheptanenitrile of 1:0.003. After stirring evenly, the primary modified molecular sieve was added to the ethylene glycol dimethacrylate solution, stirred at room temperature for 4 hours, and then the temperature was increased to 53°C at a heating rate of 15°C / min and maintained for 12 hours. After the polymerization was completed, it was washed with 50% ethanol for 6-8 times and dried to obtain the molecular sieve.

[0034] Comparative Example 1

[0035] Vinyl trimethoxysilane with a volume ratio of 1:1 to mesoporous MCM-41 molecular sieve is placed in a constant temperature shaker, kept warm at 25°C for 25 minutes, then the molecular sieve is added to the vinyl trimethoxysilane solution, stirred at a constant temperature for 4 hours, and then freeze-dried at -20°C for 6 hours to obtain a primary modified molecular sieve, and ethylene dimethacrylate is taken according to a volume ratio of primary modified molecular sieve: ethylene glycol dimethacrylate of 1:3, and azobisisoheptanenitrile is added according to a mass ratio of ethylene glycol dimethacrylate: azobisisoheptanenitrile of 1:0.005. After stirring evenly, the primary modified molecular sieve is added to the ethylene glycol dimethacrylate solution, stirred at room temperature for 3 hours, and then the temperature is increased to 52°C at a heating rate of 12°C / min and maintained for 10 hours. After the polymerization is completed, it is washed 6-8 times with 60% ethanol and dried to obtain the molecular sieve.

[0036] Comparative Example 2

[0037] The mesoporous MCM-41 molecular sieve raw material was frozen at -20°C for 6 hours, and vinyltrimethoxysilane with a volume ratio of 1:1 to the molecular sieve was placed in a constant temperature shaker, and kept warm at 25°C for 25 minutes. Subsequently, the frozen molecular sieve was added to the vinyltrimethoxysilane solution and stirred at a constant temperature for 4 hours to obtain a primary modified molecular sieve. Ethylene glycol dimethacrylate was taken at a volume ratio of primary modified molecular sieve: ethylene glycol dimethacrylate of 1:3, and azobisisoheptylonitrile was added at a mass ratio of ethylene glycol dimethacrylate: azobisisoheptylonitrile of 1:0.005. After stirring evenly, the primary modified molecular sieve was added to the ethylene glycol dimethacrylate solution, stirred at room temperature for 3 hours, and then the temperature was increased to 52°C at a heating rate of 12°C / min and maintained for 10 hours. After the polymerization was completed, it was washed with 60% ethanol for 6-8 times and dried to obtain the molecular sieve.

[0038] Comparative Example 3

[0039] The mesoporous MCM-41 molecular sieve raw material was frozen at -20°C for 6 hours, and vinyltrimethoxysilane with a volume ratio of 1:1 to the molecular sieve was placed in a constant temperature shaker, kept warm at 25°C for 25 minutes, and then the frozen molecular sieve was added to the vinyltrimethoxysilane solution, stirred at a constant temperature for 4 hours, and then freeze-dried at -20°C for 6 hours to obtain a primary modified molecular sieve, and divinylbenzene was taken according to a volume ratio of primary modified molecular sieve: divinylbenzene of 1:3, and azobisisoheptanenitrile was added according to a mass ratio of divinylbenzene: azobisisoheptanenitrile of 1:0.005. After stirring evenly, the primary modified molecular sieve was added to the divinylbenzene solution, stirred at room temperature for 3 hours, and then the temperature was increased to 52°C at a heating rate of 12°C / min and maintained for 10 hours. After the polymerization was completed, it was washed with 60% ethanol for 6-8 times and dried to obtain the molecular sieve.

[0040] Comparative Example 4

[0041] The mesoporous MCM-41 molecular sieve raw material was frozen at -20°C for 6 hours, and vinyltrimethoxysilane with a volume ratio of 1:1 to the molecular sieve was placed in a constant temperature shaker, kept warm at 25°C for 25 minutes, and then the frozen molecular sieve was added to the vinyltrimethoxysilane solution, stirred at a constant temperature for 4 hours, and then freeze-dried at -20°C for 6 hours to obtain a primary modified molecular sieve, and ethylene dimethacrylate was taken according to a volume ratio of primary modified molecular sieve: ethylene glycol dimethacrylate of 1:3, and azobisisobutyronitrile was added according to a mass ratio of ethylene glycol dimethacrylate: azobisisobutyronitrile of 1:0.005. After stirring evenly, the primary modified molecular sieve was added to the ethylene glycol dimethacrylate solution, stirred at room temperature for 3 hours, and then the temperature was increased to 68°C at a heating rate of 12°C / min and maintained for 10 hours. After the polymerization was completed, it was washed with 60% ethanol for 6-8 times and dried to obtain the molecular sieve.

[0042] The specific surface area and pore size distribution of the molecular sieves in the embodiments of the present invention and the comparative examples were measured by a low temperature high purity nitrogen adsorption instrument (Quantachrome / ASIQC0000-3). According to the nitrogen adsorption and desorption curves, the specific surface area and pore size distribution of the molecular sieves were calculated by the Brunauer-Emmett-Teller (BET) method, the t-plot method and the density functional theory (DFT) method.

[0043] Characterization of adsorption capacity: The static saturated adsorption capacity of different examples and comparative samples was determined by static adsorption experiments. 1 g of molecular sieve was quickly weighed in a weighing bottle, and the weighing bottle and a 50 mL beaker containing 10 mL of toluene were placed in a sealed container for static adsorption at 35°C for 24 hours. The static saturated adsorption capacity at the adsorption temperature was calculated. The relevant test results are shown in Table 1.

[0044] Table 1 Performance of molecular sieves prepared in Examples and Comparative Examples

[0045]

[0046] By analyzing the relevant data in Table 1, it can be seen that the present invention uses vinyltrimethoxysilane to pretreat the molecular sieve before using ethylene glycol dimethacrylate for modification, which can improve the reaction activity of the molecular sieve and is beneficial to enhancing the interaction between ethylene glycol dimethacrylate and the molecular sieve during the polymerization process.

[0047] Before the molecular sieve is modified by using ethylene glycol dimethacrylate and vinyl trimethoxysilane, the molecular sieve is subjected to freezing pretreatment. After the molecular sieve is subjected to freezing pretreatment, the molecular sieve at a relatively low temperature contacts the modifying agent at a relatively high temperature during the contact process between the molecular sieve and the modifying agent. Due to the temperature difference between the molecular sieve and the modifying agent, the low-temperature molecular sieve absorbs the heat of the modifying agent, cools down and shrinks the modifying agent, and helps the modifying agent to penetrate into the interior of the molecular sieve, thereby increasing the access amount of the hydrophobic modifying agent.

[0048] The present invention adopts ethylene glycol dimethacrylate as a hydrophobic modifier, and a dipole effect can be formed between the ester group in the molecular structure and the hydroxyl group in the molecular sieve, which helps the ethylene glycol dimethacrylate to enter the pores of the molecular sieve and increase the grafting amount.

[0049] After the polymerization of vinyltrimethoxysilane and ethylene glycol dimethacrylate is completed, the molecular sieve is washed with ethanol of different concentrations. On the one hand, the ethanol can destroy the hydrogen bonding between the hydroxyl groups inside the molecular sieve, and play the role of a pore expander, which is convenient for vinyltrimethoxysilane to modify the molecular sieve. On the other hand, the ethanol can remove the blockage of the molecular sieve pores by the polymer formed by the self-polymerization of vinyltrimethoxysilane and ethylene glycol dimethacrylate.

[0050] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for preparing a strongly adsorbing MCM-41 molecular sieve, characterized in that: The steps include: S1: Freeze the molecular sieve at -30°C to -20°C for 4-8h, take vinyltrimethoxysilane and place it in a constant temperature shaker, keep it warm at 25°C for 20-30min, then add the frozen molecular sieve to the vinyltrimethoxysilane solution, stir for 4-12h, and then freeze-dry at -20°C for 6h to obtain a primary modified molecular sieve; wherein, the modification of the molecular sieve by vinyltrimethoxysilane is a process in which the hydrolysis product of vinyltrimethoxysilane forms a covalent bond with the silanol group on the surface of the molecular sieve; S2: Evenly mix ethylene glycol dimethacrylate and azobisisoheptanenitrile to obtain an ethylene glycol dimethacrylate solution, wherein the mass ratio of ethylene glycol dimethacrylate to azobisisoheptanenitrile is 1:0.001-0.005; S3: adding the primary modified molecular sieve obtained in step S1 to the ethylene glycol dimethacrylate solution in step S2, stirring at room temperature for 2-4 hours, raising the temperature to 50-53°C at a certain heating rate, and maintaining it for 8-12 hours. After the polymerization is completed, washing with ethanol for 6-8 times and drying.

2. The method for preparing a strongly adsorbing MCM-41 molecular sieve according to claim 1, characterized in that: The MCM-41 described in step S1 is a mesoporous molecular sieve.

3. The method for preparing a strongly adsorbing MCM-41 molecular sieve according to claim 1, characterized in that: In step S1, the volume ratio of vinyltrimethoxysilane to molecular sieve is 0.8-1:

1.

4. The method for preparing a strongly adsorbing MCM-41 molecular sieve according to claim 1, characterized in that: In step S1, the freezing temperature of the molecular sieve is -20°C, and the freezing time is 6 hours.

5. The method for preparing a strongly adsorbing MCM-41 molecular sieve according to claim 1, characterized in that: In step S2, the mass ratio of ethylene glycol dimethacrylate to azobisisoheptanenitrile is 1:0.

005.

6. The method for preparing a strongly adsorbing MCM-41 molecular sieve according to claim 1, characterized in that: In step S3, the volume ratio of ethylene glycol dimethacrylate to the primary modified molecular sieve is 2-4:

1.

7. The method for preparing a strongly adsorbing MCM-41 molecular sieve according to claim 1, characterized in that: The volume concentration of ethanol in step S3 is 50%-75%.

8. The method for preparing a strong adsorption MCM-41 molecular sieve according to claim 1, characterized in that: The heating rate in step S3 is 10-15°C / min.

9. The method for preparing a strongly adsorbing MCM-41 molecular sieve according to claim 1, characterized in that: The heating rate in step S3 is 12° C. / min.

10. The method for preparing a strong adsorption MCM-41 molecular sieve according to claim 1, characterized in that: In step S3, the temperature is raised to 52°C and maintained for 10 hours.

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