Nanospherical hierarchical porous h-beta zeolite and preparation method and application thereof

Abstract

The application belongs to the technical field of nano zeolite, and particularly relates to a kind of nanometer spherical multi-level hole H-Beta zeolite and its preparation method and application.Nanometer spherical multi-level hole H-Beta zeolite of the application uses silicon source, aluminum source and microporous template agent as raw material, is obtained by controlling raw material ratio and preparation process, has micropore and double intercrystalline mesopore structure, has large external specific surface area (431~670m 2 / g) and mesopore volume (0.25~0.57cm 3 / g);The double intercrystalline mesopore structure of H-Beta zeolite of the application improves the mass transfer limitation caused by traditional zeolite only having micropore, and avoids weakening of the limitation caused by forming macropore;In the reaction of catalyzing lactic acid to synthesize propiolactone, excellent catalytic activity and stability are presented, and the generation of byproduct can be reduced, and the yield of product is improved.

Description

Technical Field

[0001] This invention belongs to the field of nanozeolite technology, specifically relating to nanospherical hierarchical porous H-Beta zeolite, its preparation method, and its application. Background Technology

[0002] Zeolites, with their excellent thermal stability, acidity, high specific surface area, and unique pore structure, are widely used in catalysis and adsorption separation. However, due to their microporous structure and small pore size (<2 nm), diffusion in the medium is restricted. Since diffusion is the primary mechanism of mass transfer, it determines the catalytic performance (activity, selectivity, and lifetime) of zeolites in many reactions and the efficiency of separation processes. This diffusion restriction in the microporous channels of zeolites also easily leads to carbon deposition and deactivation, severely affecting the catalytic activity, selectivity, and lifetime of zeolites. Hierarchical porous zeolites, with their inherent micropores and intracrystalline / intercrystalline mesopores, can effectively alleviate the diffusion restriction and steric hindrance of microporous zeolites, accelerate intercrystalline diffusion, significantly improve mass transfer rates, prevent reactants from further transforming into byproducts, thereby extending the lifetime of zeolites and improving their catalytic efficiency. Therefore, hierarchical porous zeolites containing mesopores are considered the most promising catalytic materials.

[0003] The preparation methods of hierarchical porous zeolites mainly include two strategies: bottom-up and top-down. Hard template methods and soft template methods belong to the bottom-up strategy; desilication or dealumination methods belong to the top-down strategy. In the bottom-up strategy, although the hard template method easily obtains hierarchical porous zeolites, its poor water solubility and poor mesopore connectivity result in low effective utilization of the mesopores. The soft template method has good biocompatibility with zeolites, but generally requires the use of two template agents, as described in patent CN109529921A, which uses a surfactant [C]. 12 H 25 (CH3)2N + (CH2)6N + (CH3)2C 12 H 25 [Br]2 -Using microporous templates as mesoporous templates in the synthesis of hierarchical beta zeolites not only increases the synthesis cost, but also creates competition between microporous and mesoporous templates. Top-down strategies, such as dealumination and dealsilicate methods, suffer from drawbacks like micropore loss and altered acidity in the preparation of hierarchical porous zeolites. Patent CN109847790A describes a method of obtaining hierarchical porous FAU zeolites by placing zeolites with FAU-type structures in an alkaline medium for alkali treatment followed by ammonium exchange. Furthermore, researchers have explored alternative synthesis methods, such as two-step crystallization, seeding, and steam-assisted methods. Patent CN113353952A describes a two-step synthesis method: dissolving tetraethyl orthosilicate (TES) under hydrochloric acid reflux, mixing the resulting solution with hexamethyleneimine (HMI) and sodium aluminate (TAA) to form a gel, followed by hydrothermal crystallization to obtain micron-sized hierarchical porous ZSM-5 zeolite; Patent CN113353953A uses a seed method to synthesize zeolite, followed by chemical etching with sodium hydroxide to obtain cyclic nano-hierarchical porous ZSM-5 zeolite composed of ZSM-5 nanosheets approximately 50 nm thick; Patent CN114920261A uses acid vapor to depolymerize natural illite clay, grinds it uniformly, and then employs a variable-temperature crystallization strategy to obtain nano-hierarchical porous H-Beta zeolite; Patent CN106219569A uses different silicon sources, aluminum sources, and TPA without the use of mesoporous templates. + Using a template agent, hierarchical porous ZSM-5 zeolite formed by stacking strip-shaped crystals was synthesized, with a pore size range of 5~100nm. As can be seen from the above, the synthesis of hierarchical porous zeolite is a complex and cumbersome process. Summary of the Invention

[0004] The purpose of this invention is to provide a nanosphere-shaped hierarchical porous H-Beta zeolite with good catalytic activity and stability, simple preparation, and mild conditions, as well as its preparation method and application.

[0005] The present invention provides nanosphere-shaped hierarchical porous H-Beta zeolite, which is a nanosphere aggregate obtained by using commonly used silicon sources, aluminum sources, and microporous template agents as raw materials and through simple control of raw material ratios and preparation processes. It is a nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores. The double intercrystalline mesopores have pore sizes of 5–10 nm and 12–18 nm. The single intercrystalline mesopores with pore sizes of 5–10 nm are formed by stacking zeolite nanocrystals with an average particle size of ~18 nm; the double intercrystalline mesopores with pore sizes of 12–18 nm are formed by stacking zeolite nanoaggregates with an average particle size of ~120 nm. The molar ratio of silicon to aluminum in the zeolite is (10.9–22.0):1. (~18 nm, ~120 nm, where ~ represents an approximate number, specifically 16–20 nm, 115–125 nm, see [reference]). Figure 3 ).

[0006] The prepared hierarchical porous H-Beta zeolite has a nanosphere morphology, containing intracrystalline micropores and double intercrystalline mesopores. The mesopore size of the hierarchical porous H-Beta zeolite is distributed in two ranges: 5~10 nm and 12~18 nm. The zeolite is a silica-alumina zeolite with an actual silica-alumina ratio of 10.9~22.0:1.

[0007] The nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intergranular mesopores contains 0.13 cm 3 / g~0.24cm 3 The micropore volume is 0.25 cm³ / g. 3 / g~0.57cm 3 / g mesopore volume; preferably, the pore volume of the hierarchical H-Beta zeolite is 0.46–0.79 cm³. 3 / g.

[0008] The weak acid content of the hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores is 1.31 to 4.00 mmol / g.

[0009] The strong acid content of the hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores is 0.15–0.37 mmol / g.

[0010] The preparation method of nano-spherical hierarchical porous H-Beta zeolite provided by this invention includes the following specific steps:

[0011] (1) The silicon source, aluminum source and microporous template agent are mixed and stirred at 20-80℃ to obtain Beta zeolite gel; wherein the molar ratio of silicon source, aluminum source, template agent and water is 1:(0.067-0.167):(2-4):(4-6);

[0012] (2) Aging treatment of the gel: stirring time at room temperature is 2-6 hours; preferably 2 hours at room temperature;

[0013] (3) Ammonium fluoride (NH4F) and anhydrous ethanol (CH3CH2OH) were added to the aged gel, and after hydrothermal crystallization, the solid was collected and then washed, calcined, ion-exchanged and calcined again to obtain nanospheres with micropores and double intercrystalline mesopores of multi-level porous H-Beta zeolite; wherein the amount of ammonium fluoride and anhydrous ethanol added was based on the molar ratio of silicon source: NH4F: CH3CH2OH of 1: (0.3~0.5): (0.7~1.2).

[0014] In step (1), the microporous template agent is tetraethylammonium hydroxide, the silicon source is silica, the aluminum source is sodium aluminate, and there is no mesoporous template agent.

[0015] In step (3), the preferred molar ratio of each substance in the reaction system is: silicon source: aluminum source: microporous template agent: H2O: NH4F: CH3CH2OH = 1: 0.067~0.167: 2.4: 6: 0.33: 0.8.

[0016] In step (3), the hydrothermal crystallization conditions are hydrothermal crystallization at 100-160℃ for 2-6 days.

[0017] In step (3), the specific steps of calcination are as follows: the solid after centrifugal drying is heated in a muffle furnace at a starting temperature of 20-30°C and then increased to 500-600°C at a rate of 1-3°C / min for 4-6 hours.

[0018] In step (3), the specific steps of the ion exchange are as follows: the calcined solid is added to an ammonium-containing solution of 0.5 to 1 mol / L, and the ion exchange is carried out by stirring at 60 to 80°C for 4 to 6 hours, and the ion exchange process is repeated; preferably, the ammonium ion exchange temperature is 80°C, preferably, the stirring time of the ammonium ion exchange solution is 5 hours; preferably, the ion exchange is repeated 3 times.

[0019] In step (3), the specific steps of the recalcination are as follows: the solid product obtained after ion exchange is placed in a muffle furnace for calcination, with an initial temperature of 20-30°C, and the temperature is increased to 500-600°C at a rate of 5-10°C / min. The product is then calcined in an air atmosphere for 4-6 hours to obtain nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores.

[0020] The prepared hierarchical porous H-Beta zeolite has a nanosphere morphology, containing intracrystalline micropores and double intercrystalline mesopores. The mesopore size of the hierarchical porous H-Beta zeolite is distributed in two ranges: 5-10 nm and 12-18 nm. The zeolite is a silica-alumina zeolite with an actual silica-alumina ratio of 10.9-22.0:1.

[0021] Nitrogen adsorption-desorption curves and DFT pore size distribution diagrams show that the nanosphere-shaped hierarchical porous H-Beta zeolites provided in this invention all contain abundant intercrystalline mesoporous structures, and all contain double intercrystalline mesoporous structures (5-10 nm and 12-18 nm); they also have a large external specific surface area (431-670 m²). 2 / g) and mesopore volume (0.25–0.57 cm³) 3 The total acidity was measured to be 1.68–4.20 mmol / g by ammonia temperature-programmed adsorption-desorption (NH3-TPD).

[0022] The hierarchical porous H-Beta zeolite of the present invention, which has micropores and double intercrystalline mesopores, can be applied to biomass conversion, specifically, it can be used for efficient catalysis of lactic acid to lactide.

[0023] This invention, based on commonly used raw materials and conventional operations for synthesizing H-Beta zeolite, achieves a simple and rapid controllable synthesis of nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intergranular mesoporous structures by controlling and optimizing aging time, silica-alumina ratio, and crystallization time. The double intergranular mesoporous structure, formed by the stacking of nanocrystals and nanoaggregates, improves the mass transfer limitation caused by the micropores in traditional zeolites, while avoiding the weakening of confinement effects caused by macropores. It can be used in the catalytic synthesis of lactic acid from lactide, exhibiting excellent catalytic activity and stability, reducing the formation of byproducts and increasing product yield. Example results show that the nanosphere-shaped hierarchical porous H-Beta zeolite of this invention achieves a lactic acid conversion rate of 97.5% and a lactide yield as high as 93.5% in the catalytic synthesis of lactide. When used as a catalyst in the lactic acid-to-lactide synthesis process, it can be recycled 11 times without a significant decrease in lactide yield.

[0024] The preparation method of this invention is simple to operate and has mild conditions, which is of great significance for the industrial production of multi-level porous zeolite and the catalytic synthesis of lactic acid into lactide.

[0025] This invention uses only tetraethylammonium hydroxide as a microporous template, eliminating the need for expensive mesoporous templates and resulting in lower preparation costs. It also avoids complex subsequent acid treatment, alkali treatment, steam treatment, or temperature-variable crystallization operations, making the method simpler. Attached Figure Description

[0026] Figure 1 The figures show the nitrogen adsorption-desorption curves and pore size distribution. Here, a through d represent examples H1, H2, H3, and H4, respectively.

[0027] Figure 2 The figures show the nitrogen adsorption-desorption curves and pore size distribution. Here, a through c represent examples H5, H3, and H6, respectively.

[0028] Figure 3 This is a transmission electron microscope (TEM) image of H3.

[0029] Figure 4 The yield graph of lactide synthesis using H3 recycling. Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0031] Example 1: 8.2g of silica, 1.87g of sodium aluminate, and 48.24g of tetraethylammonium hydroxide were thoroughly mixed and stirred at room temperature to obtain Beta zeolite gel. The resulting gel was aged for 2 hours. Then, 1.52g of ammonium fluoride and 5.0g of anhydrous ethanol were added to the aged gel system, and the mixture was placed in a 100mL stainless steel reactor lined with polytetrafluoroethylene. The reactor was then placed in a 140℃ oven for static crystallization at a constant temperature for 96 hours (4 days). The solid product was centrifuged, washed, and dried at 100℃ for 12 hours. The dried solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 1℃ / min to 550℃, and calcined in air for 6 hours to remove the template agent. The calcined solid was added to a 1 mol / L ammonium chloride solution and stirred at 80 °C for 5 h for ion exchange. This process was repeated 3 times and then dried. The resulting solid product was placed in a muffle furnace for calcination. Starting at 20 °C, the temperature was increased to 550 °C at a rate of 5 °C / min and calcined in air for 6 h to obtain nanosphere-shaped hierarchical porous H-Beta zeolite, designated H1.

[0032] Example 2: 8.2g of silica, 1.24g of sodium aluminate, and 48.24g of tetraethylammonium hydroxide were thoroughly mixed and stirred at room temperature to obtain Beta zeolite gel. The resulting gel was aged for 2 hours. Then, 1.52g of ammonium fluoride and 5.0g of anhydrous ethanol were added to the aged gel system, and the mixture was placed in a 100mL stainless steel reactor lined with polytetrafluoroethylene. The reactor was then placed in a 140℃ oven for static crystallization at a constant temperature for 96 hours (4 days). The solid product was centrifuged, washed, and dried at 100℃ for 12 hours. The dried solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 1℃ / min to 550℃, and calcined in air for 6 hours to remove the template agent. The calcined solid was added to a 1 mol / L ammonium chloride solution and stirred at 80 °C for 5 h for ion exchange. This process was repeated 3 times and then dried. The resulting solid product was placed in a muffle furnace for calcination. Starting at 20 °C, the temperature was increased to 550 °C at a rate of 5 °C / min and calcined in air for 6 h to obtain nanosphere-shaped hierarchical porous H-Beta zeolite, designated H2.

[0033] Example 3: 8.2g of silica, 0.93g of sodium aluminate and 48.24g of tetraethylammonium hydroxide were thoroughly mixed and stirred at room temperature to obtain Beta zeolite gel. The obtained gel was aged for 2 hours, and then 1.52g of ammonium fluoride and 5.0g of anhydrous ethanol were added to the aged gel system. The mixture was placed in a 100mL stainless steel reactor lined with polytetrafluoroethylene and then placed in an oven at 140 ℃ for static crystallization for 96 hours (4 days). The solid product was centrifuged, washed, and dried at 100℃ for 12 h. The dried solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 1℃ / min to 550℃, and calcined in air for 6 h to remove the template agent. The calcined solid was then added to a 1 mol / L ammonium chloride solution and stirred at 80℃ for 5 h for ion exchange. This process was repeated three times, followed by drying. The resulting solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 5℃ / min to 550℃, and calcined in air for 6 h to obtain nanosphere-shaped hierarchical porous H-Beta zeolite, designated H3.

[0034] Example 4: 8.2g of silica, 0.75g of sodium aluminate and 48.24g of tetraethylammonium hydroxide were thoroughly mixed and stirred at room temperature to obtain Beta zeolite gel. The obtained gel was aged for 2 hours. 1.52g of ammonium fluoride and 5.0g of anhydrous ethanol were added to the aged gel system and placed in a 100mL stainless steel reactor lined with polytetrafluoroethylene. The reactor was then placed in an oven at 140 ℃ and allowed to crystallize at a constant temperature for 96 hours (4 days). The solid product was centrifuged, washed, and dried at 100℃ for 12 h. The dried solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 1℃ / min to 550℃, and calcined in air for 6 h to remove the template agent. The calcined solid was then added to a 1 mol / L ammonium chloride solution and stirred at 80℃ for 5 h for ion exchange. This process was repeated three times, followed by drying. The resulting solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 5℃ / min to 550℃, and calcined in air for 6 h to obtain nanosphere-shaped hierarchical porous H-Beta zeolite, designated H4.

[0035] Example 5: 8.2g of silica, 0.93g of sodium aluminate and 48.24g of tetraethylammonium hydroxide were thoroughly mixed and stirred at room temperature to obtain Beta zeolite gel. The obtained gel was aged for 2 hours. 1.52g of ammonium fluoride and 5.0g of anhydrous ethanol were added to the aged gel system and placed in a 100mL stainless steel reactor lined with polytetrafluoroethylene. The reactor was then placed in an oven at 140 ℃ and allowed to crystallize at a constant temperature for 48 hours (2 days). The solid product was centrifuged, washed, and dried at 100℃ for 12 h. The dried solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 1℃ / min to 550℃, and calcined in air for 6 h to remove the template agent. The calcined solid was then added to a 1 mol / L ammonium chloride solution and stirred at 80℃ for 5 h for ion exchange. This process was repeated three times, followed by drying. The resulting solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 5℃ / min to 550℃, and calcined in air for 6 h to obtain nanospherical hierarchical porous H-Beta zeolite, designated H5.

[0036] Example 6: 8.2g of silica, 0.93g of sodium aluminate and 48.24g of tetraethylammonium hydroxide were thoroughly mixed and stirred at room temperature to obtain Beta zeolite gel. The obtained gel was aged for 2 hours. 1.52g of ammonium fluoride and 5.0g of anhydrous ethanol were added to the aged gel system and placed in a 100mL stainless steel reactor lined with polytetrafluoroethylene. The reactor was then placed in an oven at 140 ℃ and allowed to crystallize at a constant temperature for 144 hours (6 days). The solid product was centrifuged, washed, and dried at 100℃ for 12 h. The dried solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 1℃ / min to 550℃, and calcined in air for 6 h to remove the template agent. The calcined solid was then added to a 1 mol / L ammonium chloride solution and stirred at 80℃ for 5 h for ion exchange. This process was repeated three times, followed by drying. The resulting solid product was then calcined in a muffle furnace, starting at 20℃ and increasing the temperature at 5℃ / min to 550℃, and calcined in air for 6 h to obtain nanospherical hierarchical porous H-Beta zeolite designated H6.

[0037] Unless otherwise specified, the raw materials used in the embodiments of this invention were all purchased through commercial channels.

[0038] Figure 1 Nitrogen adsorption-desorption curves and DFT-calculated pore size distribution diagrams of nanosphere hierarchical porous H-Beta zeolites in Examples H1, H2, H3 and H4 (a~d); Figure 2 Nitrogen adsorption-desorption curves and DFT-calculated pore size distribution diagrams of nanospherical hierarchical porous H-Beta zeolites in Examples H5, H3 and H6 (a~c); Figure 3Table 1 shows the transmission electron microscope image of the hierarchical porous Beta zeolite H3 obtained in Example 3; Table 1 shows the pore structure data of the nanosphere hierarchical porous H-Beta zeolites obtained in Examples H1, H2, H3, H4, H5 and H6; Table 3 shows the acidity data of the nanosphere hierarchical porous H-Beta zeolites in Examples H1, H2, H3 and H4. Figure 4 A bar chart showing the yield of lactide synthesized using H3 recycling.

[0039] The Brunauer-Emmett-Teller (BET) equation was used to calculate the total specific surface area of ​​the sample. The t-plot method was used to calculate the microporous specific surface area and microporous volume of the zeolite sample. The total pore volume of the sample was obtained by using the volume of adsorbed nitrogen when P / P0 = 0.99. The mesoporous specific surface area was calculated by the difference between the total specific surface area and the microporous specific surface area. The mesoporous volume was calculated by the difference between the total pore volume and the microporous pore volume. The mesoporous distribution information of the hierarchical H-Beta zeolite was obtained by using the DFT model.

[0040] The strong and weak acid properties of the obtained nanosphere hierarchical porous zeolite were calculated using the ammonia-programmed temperature desorption (NH3-TPD) method. Table 3 shows the weak and strong acid properties obtained from the NH3-TPD data curves, calculated using the spectral analysis function of Origin software with the lowest point as the baseline.

[0041] Figure 1 These are nitrogen adsorption-desorption curves and DFT-calculated pore size distribution diagrams of nanosphere hierarchical porous H-Beta zeolites in Examples H1, H2, H3, and H4, respectively (a~d represent Examples H1, H2, H3, and H4, respectively). Figure 2 These are nitrogen adsorption-desorption curves and DFT pore size distribution diagrams of the hierarchical porous H-Beta zeolites in Examples H3, H5, and H6 (a~c represent Examples H5, H3, and H6, respectively).

[0042] Depend on Figure 1 and Figure 2 As can be seen from the nitrogen adsorption-desorption curves, the nano-spherical hierarchical porous H-Beta zeolite (Examples 1-6) prepared in this invention exhibits good performance at nitrogen adsorption-desorption rates below 0.0. P / P 0 <0.1 low P / P 0 The adsorption capacity varies with the region. P / P 0 The increase is rapid due to the filling of N2 in the micropore region; at 0.9 < P / P 0 The presence of a desorption hysteresis ring in the <1.0 region indicates the existence of mesopores in its structure, specifically intercrystalline mesopores formed by the stacking of zeolite nanoparticles or nanoaggregates. According to... Figure 1 and Figure 2The pore size distribution curve obtained by the DFT model shows that the nanosphere hierarchical porous H-Beta zeolite of the present invention has a double intercrystalline mesoporous (5~10 nm and 12~18 nm) and intracrystalline micropore (~0.5 nm) structure.

[0043] Figure 3 Field emission transmission electron microscopy characterization of the obtained Example 3 further proves that the nanosphere hierarchical porous H-Beta zeolite obtained in this invention is a double intercrystalline mesoporous zeolite with a size of 5-10 nm and 12-18 nm. The 5-10 nm pores are formed by the stacking of zeolite nanoparticles with a size of ~18 nm, and the intercrystalline mesopores with a size of 12-18 nm belong to the stacked voids of nano-aggregates with a size of ~120 nm.

[0044] Table 1 shows the pore structure data of the nanosphere hierarchical porous H-Beta zeolites of Examples H1, H2, H3, H4, H5, and H6. [a] The total specific surface area of ​​the hierarchical porous H-Beta zeolites was calculated using the Brunauer-Emmett-Teller (BET) method; [b] The micropore specific surface area of ​​the samples was calculated using the t-plot method; [c] The difference between the obtained total specific surface area and the micropore specific surface area, i.e., S... meso =S BET -S micro [d] The calculated mesoporous specific surface area; [e] The micropore volume calculated using the t-plot method; [f] The difference between the total pore volume and the micropore volume, i.e., V. meso =V pore -V micro The calculated mesopore volume; [f] The total pore volume calculated using the t-plot method.

[0045] Table 1 shows that Examples H1, H2, H3, H4, H5, and H6 prepared using the present invention are all hierarchical porous zeolites. The hierarchical porous H-Beta zeolite H1 obtained in Example 1 has a total specific surface area of ​​431 m². 2 / g, with a microporous specific surface area of ​​295 m² 2 / g, mesoporous specific surface area is 136 m² 2 / g, the total pore volume of sample H1 is 0.46 cm³. 3 / g, of which the micropore volume is 0.13 cm³ 3 / g, mesoporous pore volume is 0.33 cm³ 3 / g; The hierarchical porous H-Beta zeolite H2 obtained in Example 2 has a total specific surface area of ​​613 m². 2 / g, with a microporous specific surface area of ​​431 m² 2 / g, mesoporous specific surface area is 183 m² 2 / g, the total pore volume of the H2 sample is 0.69 cm³.3 / g, of which the micropore volume is 0.20 cm³. 3 / g, mesoporous pore volume is 0.49 cm³ 3 / g; The hierarchical porous H-Beta zeolite H3 obtained in Example 3 has a total specific surface area of ​​670 m². 2 / g, microporous specific surface area is 510 m² 2 / g, mesoporous specific surface area 160 m² 2 / g, the total pore volume of sample H3 is 0.79cm³. 3 / g, of which the micropore volume is 0.22 cm³. 3 / g, mesoporous pore volume is 0.57 cm³ 3 / g; The hierarchical porous H-Beta zeolite H4 obtained in Example 4 has a total specific surface area of ​​587 m². 2 / g, with a microporous specific surface area of ​​432m² 2 / g, mesoporous specific surface area is 154 m² 2 / g, the total pore volume of sample H4 is 0.60 cm³. 3 / g, of which the micropore volume is 0.19 cm³. 3 / g, mesoporous pore volume is 0.41 cm³ 3 / g. The hierarchical porous H-Beta zeolite H5 obtained in Example 5 has a total specific surface area of ​​668 m². 2 / g, with a microporous specific surface area of ​​577 m² 2 / g, mesoporous specific surface area is 91 m² 2 / g, the total pore volume of sample H5 is 0.54 cm³. 3 / g, of which the micropore volume is 0.23 cm³ 3 / g, mesoporous pore volume is 0.31cm³ 3 / g; The hierarchical porous H-Beta zeolite H6 obtained in Example 6 has a total specific surface area of ​​642 m². 2 / g, with a microporous specific surface area of ​​558m² 2 / g, mesoporous specific surface area 95 m² 2 / g, the total pore volume of sample H6 is 0.49 cm³. 3 / g, of which the micropore volume is 0.24 cm³. 3 / g, mesoporous pore volume is 0.25 cm³ 3 / g.

[0046] The acidity of H1, H2, H3 and H4 prepared in this invention was determined by ammonia-programmed temperature desorption (NH3-TPD), and the data are listed in Table 2. [a] The actual silica-alumina ratio of the nanosphere hierarchical porous H-Beta zeolite of this invention was obtained by inductively coupled plasma optical emission spectrometry (ICP-OES). Table 2 shows that Example H1 has a silicon-to-aluminum ratio of 10.90, and its total acid content, measured by ammonia temperature-programmed desorption, is 1.92 mmol / g, with weak acid content of 1.72 mmol / g and strong acid content of 0.20 mmol / g. Example H2 has a silicon-to-aluminum ratio of 15.40, and its total acid content, measured by ammonia temperature-programmed desorption, is 2.65 mmol / g, with weak acid content of 2.50 mmol / g and strong acid content of 0.15 mmol / g. Example H3 has a silicon-to-aluminum ratio of 16.50, and its total acid content, measured by ammonia temperature-programmed desorption, is 4.20 mmol / g, with weak acid content of 4.00 mmol / g and strong acid content of 0.20 mmol / g. Example H4 has a silicon-to-aluminum ratio of 22.00, and its total acid content, measured by ammonia temperature-programmed desorption, is 1.68 mmol / g. The content of weak acid is 1.31 mmol / g, and the content of strong acid is 0.37 mmol / g.

[0047] Test experiment: The catalytic performance of the nanosphere hierarchical porous H-Beta zeolite (H1~H6) prepared in Examples 1~6 as a catalyst in the one-step synthesis of lactic acid into lactide was investigated using a laboratory-built device.

[0048] Test evaluation: 1.0 g L A 50 wt% aqueous solution of LA, 0.5 g of the prepared hierarchical H-Beta zeolite, and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). After reacting for 3 hours, the hierarchical H-Beta zeolite was removed by filtration. The filtrate was dried over N2 to remove the toluene solvent, yielding the crude product. 1 The crude products obtained from each example catalyst were determined by 1H NMR, with lactic acid conversion and lactide yield used as evaluation indicators.

[0049] (1): 1.0 g L A 50 wt% aqueous solution of LA, 0.5 g of H1, and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). After 3 hours of reaction, the mixture was filtered, and the filtrate was dried under vacuum. The test results showed that the hierarchical porous H-Beta zeolite H1 obtained in Example 1 catalyzed the synthesis of lactic acid from lactic acid with a lactic acid conversion rate of 87% and a lactic acid yield of 67.6%.

[0050] (2): 1.0 g LA 50 wt% aqueous solution of LA, 0.5 g H2, and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). After 3 hours of reaction, the mixture was filtered, and the filtrate was dried under vacuum. The test results showed that the hierarchical porous H-Beta zeolite obtained in Example 2 catalyzed the synthesis of lactic acid from lactic acid using H2, achieving a lactic acid conversion rate of 95.3% and a lactic acid yield of 84.7%.

[0051] (3): 1.0 g L A 50 wt% aqueous solution of LA, 0.5 g H3, and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). After reacting for 3 hours, the mixture was filtered, and the filtrate was dried under vacuum. The test results showed that the hierarchical porous H-Beta zeolite obtained in Example 3 catalyzed the synthesis of lactic acid from lactide with a lactic acid conversion rate of 97.5% and a lactide yield of 93.5%.

[0052] (4): 1.0 g L A 50 wt% aqueous solution of LA, 0.5 g of H4, and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). After 3 hours of reaction, the mixture was filtered, and the filtrate was dried under vacuum. The test results showed that the hierarchical porous H-Beta zeolite H4 obtained in Example 4 catalyzed the synthesis of lactic acid from lactic acid with a lactic acid conversion rate of 97.1% and a lactic acid yield of 87.1%.

[0053] (5): 1.0 g L -50 wt% LA aqueous solution, 0.5 g of hierarchical porous H-Beta zeolite H5 obtained in Example H5, and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). After reacting for 3 hours, the mixture was filtered, and the filtrate was dried under vacuum. The test results showed that the hierarchical porous H-Beta zeolite H5 obtained in Example 5 catalyzed the synthesis of lactic acid from lactide, with a lactic acid conversion rate of 94.2% and a lactide yield of 78.7%.

[0054] (6): 1.0 g L A 50 wt% aqueous solution of LA, 0.5 g of H6, and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). After 3 hours of reaction, the mixture was filtered, and the filtrate was dried under vacuum. The test results showed that the hierarchical porous H-Beta zeolite H6 obtained in Example 6 catalyzed the synthesis of lactic acid from lactide with a lactic acid conversion rate of 91.2% and a lactide yield of 69.3%.

[0055] Catalyst recycling evaluation

[0056] 1.0 g L- 50 wt% LA aqueous solution, 0.5 g of hierarchical H-Beta zeolite H3 obtained in Example 3, and 10 mL of toluene were added to a 25 mL round-bottom flask and reacted in an oil bath (140 °C). After reacting for 3 hours, the hierarchical H-Beta zeolite H3 was filtered off. (a) The filtered hierarchical H-Beta zeolite H3 was calcined in a muffle furnace at 550 °C for 4 h to remove organic matter, and then reacted with 1.0 g of... L - An aqueous solution of LA (50 wt%) and 10 mL of toluene were added to a 25 mL round-bottom flask, and the reaction was carried out in an oil bath (140 °C). Step (a) was repeated 10 times, and the yield of lactide obtained by repeated use of the catalyst was as follows. Figure 4 As shown, the hierarchical porous H-Beta zeolite H3 prepared in this invention did not show a significant decrease in the yield of lactic acid to lactide after being reused 11 times.

[0057] Table 1 shows the pore structure data of the nanosphere hierarchical porous H-Beta zeolite in the examples.

[0058] sample <![CDATA[S BET a (m 2 / g)]]> <![CDATA[S Micro b (m 2 / g)]]> <![CDATA[S Meso c (m 2 / g)]]> <![CDATA[V Micro d (cm 3 / g)]]> <![CDATA[V Meso e (cm 3 / g)]]> <![CDATA[V Total f (cm 3 / g)]]> H1 431 295 136 0.13 0.33 0.46 H2 613 431 183 0.20 0.49 0.69 H3 670 510 160 0.22 0.57 0.79 H4 587 432 154 0.19 0.41 0.60 H5 668 577 91 0.23 0.31 0.54 H6 642 558 95 0.24 0.25 0.49 .

[0059] Table 2 shows the H-Beta zeolite content data of the nanosphere hierarchical porous zeolite samples.

[0060] sample <![CDATA[Silica-alumina ratio a > Acidity of weak acid (mmol / g) Acid strength of strong acids (mmol / g) Total acidity (mmol / g) H1 10.90 1.72 0.20 1.92 H2 15.40 2.50 0.15 2.65 H3 16.50 4.00 0.20 4.20 H4 22.00 1.31 0.37 1.68 .

Claims

1. A nanospherical hierarchical porous H-Beta zeolite, characterized in that, The zeolite is a nanosphere aggregate obtained by controlling the raw material ratio and preparation process using silicon, aluminum, and microporous template agents. It is a nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores. The double intercrystalline mesopores have pore sizes of 5-10 nm and 12-18 nm. The single intercrystalline mesopores with pore sizes of 5-10 nm are formed by stacking zeolite nanocrystals with an average particle size of ~18 nm. The double intercrystalline mesopores with pore sizes of 12-18 nm are formed by stacking zeolite nanoaggregates with an average particle size of ~120 nm. The molar ratio of silicon to aluminum in the zeolite is (10.9-22.0):

1. The micropore volume is 0.13 cm³. 3 / g~0.24cm 3 / g, mesopore volume is 0.25cm³ 3 / g~0.57cm 3 / g; weak acid strength is 1.31–4.00 mmol / g; strong acid strength is 0.15–0.37 mmol / g; Specifically, it is prepared by the following steps: (1) The silicon source, aluminum source and microporous template agent are mixed and stirred at 20-80℃ to obtain Beta zeolite gel; wherein the molar ratio of silicon source, aluminum source, template agent and water is 1:(0.067-0.167):(2-4):(4-6); The microporous template agent is tetraethylammonium hydroxide, the silicon source is silica, and the aluminum source is sodium aluminate; (2) Aging treatment of the gel: stirring time at room temperature for 2-6 hours; (3) Ammonium fluoride and anhydrous ethanol were added to the aged gel, and the gel was subjected to hydrothermal crystallization. The solid was then collected, washed, calcined, ion-exchanged, and calcined again to obtain nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores. The amount of ammonium fluoride and anhydrous ethanol added was based on a molar ratio of silicon source: NH4F: CH3CH2OH of 1: (0.3-0.5): (0.7-1.2). The hydrothermal crystallization conditions are: hydrothermal crystallization at 100–160°C for 2–6 days; The specific steps of the calcination are as follows: the centrifugally dried solid is placed in a muffle furnace at an initial temperature of 20-30°C, and the temperature is increased to 500-600°C at a rate of 1-3°C / min for 4-6 hours. The specific steps of the ion exchange are as follows: the calcined solid is added to an ammonium-containing solution of 0.5-1 mol / L, and the mixture is stirred at 60-80℃ for 4-6 hours to carry out ion exchange, and the ion exchange process is repeated. The specific steps of the recalcination are as follows: the solid product obtained after ion exchange is placed in a muffle furnace for calcination, with an initial temperature of 20-30°C, and the temperature is increased to 500-600°C at a rate of 5-10°C / min. The product is then calcined in an air atmosphere for 4-6 hours to obtain nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores.

2. A method for preparing nanospherical hierarchical porous H-Beta zeolite as described in claim 1, characterized in that, The specific steps are as follows: (1) The silicon source, aluminum source and microporous template agent are mixed and stirred at 20-80℃ to obtain Beta zeolite gel; wherein the molar ratio of silicon source, aluminum source, template agent and water is 1:(0.067-0.167):(2-4):(4-6); The microporous template agent is tetraethylammonium hydroxide, the silicon source is silica, and the aluminum source is sodium aluminate; (2) Aging treatment of the gel: stirring time at room temperature for 2-6 hours; (3) Ammonium fluoride and anhydrous ethanol were added to the aged gel, and the gel was subjected to hydrothermal crystallization. The solid was then collected, washed, calcined, ion-exchanged, and calcined again to obtain nanosphere-shaped hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores. The amount of ammonium fluoride and anhydrous ethanol added was based on a molar ratio of silicon source: NH4F: CH3CH2OH of 1: (0.3-0.5): (0.7-1.2). The hydrothermal crystallization conditions are: hydrothermal crystallization at 100–160°C for 2–6 days; The specific steps of the calcination are as follows: the centrifugally dried solid is placed in a muffle furnace at an initial temperature of 20-30°C, and the temperature is increased to 500-600°C at a rate of 1-3°C / min for 4-6 hours. The specific steps of the ion exchange are as follows: the calcined solid is added to an ammonium-containing solution of 0.5-1 mol / L, and the mixture is stirred at 60-80℃ for 4-6 hours to carry out ion exchange, and the ion exchange process is repeated. The specific steps of the recalcination are as follows: the solid product obtained after ion exchange is placed in a muffle furnace for calcination. The initial temperature is 20-30℃, and the temperature is increased to 500-600℃ at a rate of 5-10℃ / min. The product is then calcined in air for 4-6 hours to obtain nano-spherical hierarchical porous H-Beta zeolite with micropores and double intercrystalline mesopores.

3. The application of the nanospherical hierarchical porous H-Beta zeolite as described in claim 1 in the efficient catalytic conversion of lactic acid to lactide.

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