Composite molecular sieve, method for preparing the same, and use thereof

Abstract

The application provides a composite molecular sieve and a preparation method and application thereof, and belongs to the technical field of molecular sieve materials. The application first prepares pretreated SBA-15, uses ultrasonic dispersion and stirring treatment to promote the full diffusion of multi-functional POSS into the mesoporous interior of SBA-15, and under the action of a catalyst, condensation reaction occurs between the two, a large amount of free silicon hydroxyl in SBA-15 is consumed, the erosion of water vapor on the skeleton of SBA-15 at high temperature is inhibited, the overall crosslinking density is improved, the POSS cage introduced can also constrain the extension of micro-cracks, absorb friction impact energy, improve the compression resistance and wear resistance of the composite molecular sieve carrier, the fluidized bed is not easy to be pulverized for a long time, the service life is prolonged, the physical barrier formed by the POSS cage greatly reduces the loss of active components, the recycling service life is improved, the pore channel confinement and size screening effect are formed, the hydrogen transfer side reaction is inhibited, and the selectivity of propylene and butene low-carbon olefins is improved.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve materials technology, and in particular to a composite molecular sieve, its preparation method, and its application. Background Technology

[0002] SBA-15 mesoporous molecular sieves possess regular hexagonal ordered tubular mesopores (pore size 5~12nm), ultra-high specific surface area, and large pore volume, making them an excellent support for heterogeneous catalysis and gas adsorption. However, the pore walls of SBA-15 are amorphous SiO2, with a large number of free Si-OH silanol groups on the inner walls. In high-temperature steam and aqueous methanol reaction systems, water molecules form hydrogen bonds with Si-OH, continuously hydrolyzing and breaking Si-O-Si silicon-oxygen bonds. The ordered hexagonal mesoporous structure gradually disintegrates, pores collapse, specific surface area and pore volume decrease significantly, and the catalyst deactivates rapidly. Furthermore, the amorphous silica walls of SBA-15 have poor mechanical toughness. Under slurry liquid-phase catalysis and high-temperature fluidized bed conditions, continuous friction and collision between particles make the support extremely prone to breakage and pulverization. Fine powders easily clog reaction pipelines and separation equipment, and the pulverization damages the mesoporous structure, leading to a rapid decline in catalytic performance. In addition, the inner wall of pure silicon SBA-15 contains only inert Si-OH, which has weak interaction with the impregnated metal and metal oxide active components. It relies solely on weak physical adsorption. Under high-temperature reaction conditions, metal nanoparticles are prone to migration, agglomeration and growth. Moreover, under the continuous action of solvent rinsing and water vapor, the active components are easily dissolved and lost, and the catalytic activity is greatly reduced after multiple cycles. Summary of the Invention

[0003] The purpose of this invention is to provide a composite molecular sieve, its preparation method, and its application. The method provided by this invention utilizes multifunctional POSS to modify SBA-15 to prepare a composite molecular sieve. This process consumes a large amount of free silanol groups in SBA-15, strengthens the amorphous silicon walls, inhibits the erosion of the SBA-15 framework by water vapor at high temperatures, and increases the overall crosslinking density. The introduced POSS cages can constrain the extension of microcracks and absorb frictional impact energy, thereby improving the compressive strength and wear resistance of the composite molecular sieve as a carrier. It is also less prone to pulverization during long-term fluidized bed operation, extending its service life. The POSS cages form a physical barrier, limiting the migration and diffusion of subsequently loaded metal particles, significantly reducing the leaching and loss of active components, and improving the cycle life of the catalyst prepared from the composite molecular sieve.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a composite molecular sieve, comprising the following steps: SBA-15, dilute hydrochloric acid and ethanol were mixed and heated under reflux, then washed and dried in sequence to obtain pretreated SBA-15. The pretreated SBA-15, multifunctional POSS and solvent were mixed and then subjected to ultrasonic dispersion and stirring treatment in sequence to obtain a mixture; After mixing the mixture and the catalyst, a condensation reaction and post-treatment are carried out in sequence to obtain a composite molecular sieve.

[0005] Preferably, the heating reflux time is 30~90 minutes.

[0006] Preferably, the multifunctional group POSS is at least one of trisilyl isobutyl-cage polysilsesquioxane, trisilyl isooctyl-cage polysilsesquioxane, trisilyl phenyl-cage polysilsesquioxane, and tetrasilyl phenyl-cage polysilsesquioxane.

[0007] Preferably, the solvent is at least one of anhydrous toluene, tetrahydrofuran, and dichloromethane.

[0008] Preferably, the mass ratio of the pretreated SBA-15 to the multifunctional POSS is 1:(0.5~0.40).

[0009] Preferably, the ultrasonic dispersion time is 25-45 minutes, and the stirring treatment time is 3-5 hours.

[0010] Preferably, when the catalyst is dilute hydrochloric acid or p-toluenesulfonic acid, the temperature of the condensation reaction is 80~110℃, and the time of the condensation reaction is 12~24h.

[0011] Preferably, when the catalyst is triethylamine or ammonia, the temperature of the condensation reaction is 60~90°C, and the time of the condensation reaction is 6~14h.

[0012] The present invention also provides a composite molecular sieve prepared by the preparation method described in the above technical solution.

[0013] The present invention also provides an application of the composite molecular sieve described above in the preparation of catalysts and / or adsorbents.

[0014] This invention provides a method for preparing a composite molecular sieve. First, SBA-15, dilute hydrochloric acid, and ethanol are mixed and heated under reflux, followed by washing and drying to obtain pretreated SBA-15. The pretreated SBA-15, multifunctional POSS, and solvent are mixed and then subjected to ultrasonic dispersion and stirring to obtain a mixture. The mixture is then mixed with a catalyst and subjected to condensation reaction and post-treatment to obtain a composite molecular sieve. This invention first pre-treats and activates SBA-15 to expose the silanol groups on the inner wall. Ultrasonic dispersion and stirring are then used to promote the full diffusion of multifunctional POSS into the mesopores of SBA-15. Then, under the action of a catalyst, the silanol groups in the multifunctional POSS and the silanol groups in the modified SBA-15 undergo a condensation reaction to form covalent bonds, which are stably fixed on the inner wall of the mesopores. This process consumes a large amount of free silanol groups in SBA-15, strengthens the amorphous silicon wall, inhibits the erosion of the SBA-15 skeleton by moisture at high temperatures, and increases the overall crosslinking density. The introduced POSS cage can also constrain microcrack propagation and absorb frictional impacts. The energy enhances the compressive strength and wear resistance of the prepared composite molecular sieve as a carrier, making the fluidized bed formed by the composite molecular sieve less prone to pulverization during long-term fluidization, thus extending its service life. Furthermore, the POSS cage forms a physical barrier, limiting the migration and diffusion of subsequently loaded metal particles, significantly reducing the leaching and loss of active components, and improving the cycle life of the catalyst prepared from the composite molecular sieve. It also forms a pore confinement and size sieving effect, suppressing hydrogen transfer side reactions and improving the selectivity of propylene, butene, and low-carbon olefins. It can be directly used as a carrier for methanol-to-propylene / butene, CO2 adsorption, and organic fine catalysis. The process is mild and can be mass-produced and applied. Attached Figure Description

[0015] Figure 1 This is a statistical line graph showing the methanol conversion rate of the composite molecular sieves prepared in Examples 1-3 and the SBA-15 prepared in Comparative Examples 1-3 as supports for the preparation of corresponding composite catalysts for methanol conversion in this invention. Figure 2 This is a statistical graph showing the selectivity of the composite molecular sieves prepared in Examples 1-3 and SBA-15 prepared in Comparative Examples 1-3 as supports for the methanol conversion of the corresponding composite catalysts. Detailed Implementation

[0016] This invention provides a method for preparing a composite molecular sieve, comprising the following steps: SBA-15, dilute hydrochloric acid and ethanol were mixed and heated under reflux, then washed and dried in sequence to obtain pretreated SBA-15. The pretreated SBA-15, multifunctional POSS and solvent were mixed and then subjected to ultrasonic dispersion and stirring treatment in sequence to obtain a mixture; After mixing the mixture and the catalyst, a condensation reaction and post-treatment are carried out in sequence to obtain a composite molecular sieve.

[0017] Unless otherwise specified, all raw materials used in this invention are commercially available products in the art.

[0018] In this invention, the dilute hydrochloric acid is preferably a 1 mol / L HCl solution; the mass ratio of SBA-15 to the volume of dilute hydrochloric acid is preferably 10 g : (35~80) mL. In this invention, the reflux heating time is preferably 30~90 min. This invention controls the reflux heating time to fully activate SBA-15, exposing the silanol groups on the inner wall, facilitating subsequent POSS reactions with multifunctional groups. In this invention, the washing is preferably performed with deionized water until the washing solution is neutral. This invention does not have special limitations on the drying method; methods well-known in the art can be used to remove residual solvent.

[0019] In this invention, the multifunctional POSS is preferably at least one selected from trisilyl isobutyl-cage polysilsesquioxane, trisilyl isooctyl-cage polysilsesquioxane, trisilyl phenyl-cage polysilsesquioxane, and tetrasilyl phenyl-cage polysilsesquioxane. In this invention, the solvent is at least one selected from anhydrous toluene, tetrahydrofuran, and dichloromethane. In this invention, the mass ratio of the pretreated SBA-15 to the multifunctional POSS is preferably 1:(0.5~0.40), more preferably 1:(0.10~0.30). This invention controls the mass ratio of pretreated SBA-15 and multifunctional POSS to facilitate the uniform dispersion of POSS monomolecules on the pore walls, ensuring the channels remain open and can support an effective amount of active components. This adjusts molecular diffusion resistance and size sieving selectivity, improves adsorption performance, suppresses hydrogen transfer side reactions, and enhances the selectivity for propylene, butene, and other low-carbon olefins. Simultaneously, it passivates silanol groups, improves hydrothermal stability, prevents collapse of the high-temperature water vapor carrier, extends catalyst lifetime, and the rigid POSS enhances the mechanical strength of the support, making it suitable for high-temperature catalysis in fluidized beds and fixed beds. In this invention, the ultrasonic dispersion time is preferably 25-45 min, and the stirring treatment time is preferably 3-5 h. By coordinating and controlling the ultrasonic dispersion and stirring treatment times with the aforementioned solvents, this invention promotes the entry of multifunctional POSS into the mesopores of pretreated SBA-15 and their uniform distribution within the mesopores, facilitating subsequent reactions and achieving better modification effects, thus preparing a composite molecular sieve with high overall performance.

[0020] In this invention, when the catalyst is dilute hydrochloric acid or p-toluenesulfonic acid, the preferred temperature of the condensation reaction is 80-110°C, and the preferred time of the condensation reaction is 12-24 hours. In this invention, the mass ratio of SBA-15 to the dilute hydrochloric acid or p-toluenesulfonic acid is 10:(0.005-0.15). When using the above-mentioned dilute hydrochloric acid or p-toluenesulfonic acid as a catalyst, by controlling the temperature and time of the condensation reaction within the above range, the multifunctional POSS and pretreated SBA-15 can be fully reacted without damaging the ordered mesopores of SBA-15, and stably fixed on the inner wall of the mesopores of the pretreated SBA-15, achieving a better modification effect.

[0021] In this invention, when the catalyst is triethylamine or ammonia, the preferred temperature of the condensation reaction is 60-90°C, and the preferred time is 6-14 hours. By using triethylamine or ammonia as the catalyst, controlling the temperature and time of the condensation reaction within the above range promotes the full reaction of the multifunctional POSS and the pretreated SBA-15, stably fixing them onto the mesoporous inner wall of the pretreated SBA-15, thus achieving a better modification effect. In this invention, the post-treatment preferably includes: solid-liquid separation of the condensation reaction product, followed by Soxhlet extraction with tetrahydrofuran for 6-12 hours, and vacuum drying to obtain the composite molecular sieve. This invention removes unreacted free multifunctional POSS through Soxhlet extraction, ensuring smooth channels in the prepared composite molecular sieve, which is beneficial for subsequent loading of active components.

[0022] This invention first prepares pretreated SBA-15, using ultrasonic dispersion and stirring to promote the full diffusion of multifunctional POSS into the mesopores of SBA-15. Under the action of a catalyst, the two undergo a condensation reaction, consuming a large amount of free silanol groups in SBA-15, inhibiting the erosion of the SBA-15 skeleton by water vapor at high temperatures, and increasing the overall crosslinking density. The introduced POSS cages can also constrain the extension of microcracks, absorb frictional impact energy, and improve the compressive strength and wear resistance of the composite molecular sieve carrier, making it less prone to pulverization during long-term fluidized bed operation and extending its service life. Furthermore, the POSS cages form a physical barrier, significantly reducing the dissolution and loss of active components, improving the cycle life, and also forming a pore confinement and size sieving effect, inhibiting hydrogen transfer side reactions, and improving the selectivity of propylene, butene, and other low-carbon olefins.

[0023] The present invention also provides a composite molecular sieve prepared by the preparation method described in the above technical solution.

[0024] The present invention also provides an application of the composite molecular sieve described above in the preparation of catalysts and / or adsorbents.

[0025] In this invention, the catalyst is preferably a catalyst for the production of propylene / butene from methanol. In this invention, the adsorbent is preferably a CO2 adsorption and separation agent.

[0026] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0028] Example 1 A method for preparing a composite molecular sieve, comprising the following steps: 10g of SBA-15, 70mL of 1mol / L HCl solution and 150mL of ethanol were mixed and heated under reflux. The mixture was then washed with deionized water until the washing solution was neutral and dried to obtain pretreated SBA-15. The preferred mass ratio of SBA-15 to dilute hydrochloric acid is 10g:70mL. The pretreated SBA-15, multifunctional POSS and 120 mL of solvent toluene were mixed and ultrasonically dispersed for 30 min, and then stirred at room temperature for 4 h to obtain a mixture. The mass ratio of the pretreated SBA-15 to the multifunctional POSS is 1:0.20; The mixture was mixed with 0.02 g of p-toluenesulfonic acid catalyst and subjected to a condensation reaction at 100 °C for 18 h. The product of the condensation reaction was then subjected to solid-liquid separation and Soxhlet extraction with 120 mL of tetrahydrofuran for 6 h. The product was then vacuum dried to obtain the composite molecular sieve.

[0029] Example 2 The composite molecular sieve was prepared according to the method of Example 1, except that the mass ratio of the pretreated SBA-15 and the multifunctional POSS was 1:0.15.

[0030] Example 3 The composite molecular sieve was prepared according to the method of Example 1, except that the mass ratio of the pretreated SBA-15 and the multifunctional POSS was 1:0.35.

[0031] Comparative Example 1 Modified SBA-15 molecular sieves were prepared according to the method of Example 1, except that Soxhlet extraction was omitted from Example 1.

[0032] Comparative Example 2 Modified SBA-15 molecular sieves were prepared according to the method of Example 1, except that ultrasonic dispersion was omitted from Example 1.

[0033] Comparative Example 3 10g of SBA-15, 70mL of 1mol / L HCl solution and 150mL of ethanol were mixed and heated under reflux. The mixture was then washed with deionized water until the washing solution was neutral and dried to obtain pretreated SBA-15.

[0034] Application Example 1 The composite molecular sieve prepared in Example 1 was ground as a carrier, dried in an oven at 120°C for 4 hours, and then cooled to room temperature to obtain dried composite molecular sieve powder. 10 mL of zirconium salt aqueous solution was added dropwise and evenly to 10 g of dry composite molecular sieve powder while stirring to ensure that the powder was completely wetted and free of dry material. The powder was allowed to stand at room temperature for 12 h for aging. Then, the temperature was raised to 80 °C and held for 6 h, and then raised to 110 °C and held for 12 h to slowly evaporate the moisture and prevent the salt from agglomerating and clogging the pores. The powder was then calcined in a muffle furnace in an air atmosphere at a heating rate of 2 °C / min to 550 °C for 6 h. After natural cooling, white ZrO2 / SBA-15 intermediate powder was obtained. The ZrO2 / SBA-15 intermediate powder was dried at 120℃ for 3 h, and then 10 mL of diammonium hydrogen phosphate aqueous solution was uniformly added dropwise to the ZrO2 / SBA-15 intermediate powder. The powder was thoroughly stirred and moistened, sealed and allowed to stand at room temperature for 8 h, then heated to 80℃ and held for 4 h, then heated to 110℃ and held for 10 h. The powder was then calcined in an air atmosphere in a muffle furnace at a heating rate of 2℃ / min to 500℃ and held for 5 h to achieve impregnation of phosphorus and zirconium active components, thus preparing a composite catalyst for methanol conversion. The method of methanol conversion using a fixed-bed catalytic composite catalyst is as follows: In a micro-fixed bed packed with a composite catalyst for methanol conversion, the reaction temperature was adjusted to 450 °C and the methanol mass hourly space velocity (MHSV) to 300 h⁻¹. -1 The molar ratio of water to methanol was 0.8, and the pressure was atmospheric pressure. The gas phase composition of the product was analyzed by gas chromatography, and the results are shown in Table 1.

[0035] Following the method of Application Example 1, composite molecular sieves prepared in Examples 2 and 3 and SBA-15 molecular sieves prepared in Comparative Examples 1-3 were used as supports to prepare corresponding composite catalysts for methanol conversion. These catalysts were then used to catalyze methanol conversion, and the methanol conversion results were analyzed using the same method. The analytical results are shown in Table 1 and [Table data missing]. Figure 1 , 2 As shown.

[0036] Table 1. Statistical analysis of the catalytic performance of composite catalysts for methanol conversion prepared using the composite molecular sieves prepared in Examples 1-3 and SBA-15 prepared in Comparative Examples 1-3 as supports.

[0037] In summary, compared with the comparative example, the composite molecular sieve prepared in this invention, used as a support, significantly improves the catalytic performance of the composite catalyst for methanol conversion, with a significantly increased selectivity for butene and propylene. The composite molecular sieve prepared in this invention possesses pore confinement and size sieving effects, which can suppress hydrogen transfer side reactions and enhance the selectivity for propylene, butene, and other low-carbon olefins. It can be directly used as a catalytic support for methanol-to-propylene / butene production, with a mild process and suitable for large-scale production applications.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 method for preparing a composite molecular sieve, characterized in that, Includes the following steps: SBA-15, dilute hydrochloric acid and ethanol were mixed and heated under reflux, then washed and dried in sequence to obtain pretreated SBA-15. The pretreated SBA-15, multifunctional POSS and solvent were mixed and then subjected to ultrasonic dispersion and stirring treatment in sequence to obtain a mixture; After mixing the mixture and the catalyst, a condensation reaction and post-treatment are carried out in sequence to obtain a composite molecular sieve.

2. The preparation method according to claim 1, characterized in that, The heating and reflux time is 30~90 minutes.

3. The preparation method according to claim 1, characterized in that, The multifunctional group POSS is at least one of trisilyl isobutyl-cage polysilsesquioxane, trisilyl isooctyl-cage polysilsesquioxane, trisilyl phenyl-cage polysilsesquioxane, and tetrasilyl phenyl-cage polysilsesquioxane.

4. The preparation method according to claim 1, characterized in that, The solvent is at least one of anhydrous toluene, tetrahydrofuran, and dichloromethane.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the pretreated SBA-15 to the multifunctional group POSS is 1:(0.5~0.40).

6. The preparation method according to claim 1, characterized in that, The ultrasonic dispersion time is 25-45 minutes, and the stirring treatment time is 3-5 hours.

7. The preparation method according to claim 1, characterized in that, When the catalyst is dilute hydrochloric acid or p-toluenesulfonic acid, the temperature of the condensation reaction is 80~110℃, and the time of the condensation reaction is 12~24h.

8. The preparation method according to claim 1, characterized in that, When the catalyst is triethylamine or ammonia, the temperature of the condensation reaction is 60~90℃, and the time of the condensation reaction is 6~14h.

9. A composite molecular sieve prepared by the preparation method according to claims 1 to 8.

10. The use of the composite molecular sieve of claim 9 in the preparation of catalysts and / or adsorbents.

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