Preparation method of rice hull-based Y-type molecular sieve with superlarge pore volume and equal pore size

Abstract

The present application relates to a kind of preparation grade hole Y type molecular sieve with rice hull as raw material, belong to molecular sieve material preparation technical field.The method with rice hull as silicon source and carbon source, by pyrolysis and alkali activation treatment to rice hull, under the condition of not washing activated product, construct carbon-containing molecular sieve synthesis system;On this basis, by regulating aluminum source adding mode and precursor gel composition, and introduce the step of suction filtration before hydrothermal crystallization to adjust the free mother liquor content in system, to control the nucleation, growth and crystal accumulation behavior of molecular sieve.After hydrothermal crystallization and calcination to remove rice hull carbon template, the grade hole Y type molecular sieve with micropore and intercrystalline mesopore coexist can be obtained.The method does not need additional organic template or complex post-processing step, raw material source is widely, low cost, process is simple, can realize the controllable synthesis of grade hole Y type molecular sieve.The molecular sieve obtained by the present application has higher external specific surface (102 m 2 / g) and extremely high total pore volume (1.21 cm 3 / g) and external pore volume (0.97 cm 3 / g).

Description

Technical Field

[0001] This invention relates to the field of molecular sieve material preparation technology, specifically to a method for preparing hierarchical Y-type molecular sieves using rice husks as raw material, and particularly to the use of activated rice husk char to regulate the synthesis of molecular sieves, and to regulate the nucleation, growth and structural evolution of molecular sieves through a hydrothermal crystallization process to obtain Y-type molecular sieves with well-developed hierarchical pore structures. Background Technology

[0002] Zeolite molecular sieves, especially Y-type molecular sieves (FAU structure), are widely used in fluidized catalytic cracking and other fields due to their excellent thermal stability and acidic characteristics. However, traditional Y-type molecular sieves are mainly microporous, which easily leads to diffusion restriction and carbon deposition problems in macromolecular reaction systems. To improve their mass transfer performance, researchers have proposed constructing hierarchical porous molecular sieves with mesoporous or macroporous structures. Currently, these methods mainly employ post-treatment or template methods. Post-treatment methods tend to destroy the framework structure, while template methods have certain advantages in terms of structure preservation.

[0003] In template methods, traditional template materials are costly and cause significant environmental pollution. Therefore, the preparation of carbon-based hard templates using biomass resources has attracted widespread attention. Rice husks, as a widely available and inexpensive agricultural byproduct, are considered an ideal raw material for preparing molecular sieve materials, as their main components include biomass carbon and silicon dioxide. The applicant has previously disclosed and authorized a method for preparing hierarchical pore Y-type molecular sieves using rice husks as raw material (CN 108249456 B). This method involves pyrolysis and alkali activation of rice husks, using rice husk carbon as a mesoporous template and rice husk silicon as a silicon source. Under hydrothermal conditions, Y-type molecular sieves with a certain hierarchical pore structure were successfully prepared, effectively realizing the comprehensive utilization of rice husk resources.

[0004] However, further research revealed that under traditional hydrothermal crystallization conditions, continuous crystal growth and maturation easily occur during the crystallization process of molecular sieves, and the spatial matching relationship between the crystals and the carbon template changes with the crystallization process. The high water content in the system facilitates mass migration and crystal rearrangement, thereby weakening the restrictive effect of the carbon template on crystal size and packing mode. This leads to increased grain size and denser intergranular packing, which is detrimental to the effective construction of intergranular mesopores and hierarchical pore structures, thus limiting the mesoporous structure of the resulting molecular sieve (total pore volume is only 0.31 cm³). 3 / g).

[0005] Therefore, how to achieve the green and low-cost preparation of Y-type molecular sieves with well-developed hierarchical pore structures by rationally controlling the synthesis and crystallization process while maintaining the stability of the crystal structure and crystallinity of Y-type molecular sieves, and reducing the influence of unfavorable crystallization conditions on the formation of hierarchical pore structures, remains a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of this, the present invention aims to provide a method for preparing hierarchical porous Y-type molecular sieves using rice husks as raw material. By regulating the molecular sieve synthesis and crystallization process, the method promotes the formation of intercrystalline mesopores and hierarchical pore structures, thereby achieving green and low-cost preparation of hierarchical porous Y-type molecular sieves. The present invention provides a method for preparing hierarchical porous Y-type molecular sieves by utilizing activated rice husk char in the molecular sieve synthesis and by rationally controlling the water content of the synthesis system before crystallization to inhibit excessive crystal growth, thereby adjusting the crystal size and its stacking pattern and promoting the effective construction of intercrystalline mesopore structures. This method does not require the introduction of additional organic template agents or complex post-processing steps, which is beneficial for achieving green and low-cost preparation of hierarchical porous Y-type molecular sieves.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: (1) Pyrolysis and alkali activation of rice husks to obtain activated rice husk char. The product is not washed after alkali activation in order to retain the alkaline substances and silicon species for subsequent molecular sieve synthesis. (2) The activated rice husk char obtained in step (1) is mixed with deionized water and heated and stirred. After cooling, an aluminum source is added to form a carbon-containing seed gel, and after aging, a carbon-seed gel system is obtained. (3) Add aluminum source and water to the carbon-seed gel system obtained in step (2) to obtain a mixture of molecular sieve precursor gel and rice husk carbon; (4) The precursor gel obtained in step (3) is separated by filtration to remove the excess free liquid phase on the outer layer of rice husk carbon. Then the wet gel is subjected to hydrothermal crystallization to obtain carbon-molecular sieve complex. (5) The carbon-molecular sieve composite obtained in step (4) is washed, dried and calcined to remove the rice husk carbon template and obtain graded pore Y-type molecular sieve.

[0008] The alkali activation preferably uses sodium hydroxide as the alkali source; the aluminum source is preferably one or more of aluminum powder, sodium aluminate, aluminum hydroxide or aluminum sulfate.

[0009] Preferably, the rice husk pyrolysis temperature in step (1) is 350-450 °C. o C, Alkali activation at 700-900°C under an inert atmosphere. o C proceeds.

[0010] Preferably, the molar ratio of each component in the carbon-containing seed gel in step (2) is Na2O : Al2O3 : SiO2 : H2O = (15-20) : 1 : (15-25) : (300-450), The aging temperature is 20-40 degrees Celsius. oC, aging time is 12-48 hours.

[0011] Preferably, the molar ratio of SiO2 / Al2O3 in the molecular sieve precursor gel in step (3) is 8-16.

[0012] Preferably, the hydrothermal crystallization temperature in step (4) is 70-100°C. o C, crystallization time is 12-36 hours.

[0013] The hierarchical pore Y-type molecular sieve prepared by the present invention is formed by the aggregation of nano Y-type molecular sieve crystals and has a hierarchical pore structure in which micropores and intercrystalline mesopores coexist, which is beneficial to achieving a well-developed pore system while maintaining the stability of the Y-type molecular sieve crystal structure.

[0014] The raw materials used in this invention are widely available and inexpensive, require no additional organic template agents, and the synthesis process is simple and controllable, meeting the requirements of green chemistry and sustainable development, and has good potential for industrial application. Attached Figure Description

[0015] Figure 1 The XRD pattern of the graded-pore Y-type molecular sieve obtained in Example 1; Figure 2 The N2 adsorption-desorption isotherm diagram of the graded pore Y-type molecular sieve obtained in Example 1; Figure 3 This is a scanning electron microscope image of the hierarchical pore Y-type molecular sieve obtained in Example 1; Figure 4 The image shows the XRD pattern of the graded-pore Y-type molecular sieve obtained in Example 2. Figure 5 The N2 adsorption-desorption isotherm diagram of the graded pore Y-type molecular sieve obtained in Example 2; Figure 6 This is a scanning electron microscope image of the hierarchical pore Y-type molecular sieve obtained in Example 2; Figure 7 The XRD pattern of the graded-pore Y-type molecular sieve obtained in Example 3; Figure 8 The N2 adsorption-desorption isotherm diagram of the graded pore Y-type molecular sieve obtained in Example 3; Figure 9 This is a scanning electron microscope image of the hierarchical pore Y-type molecular sieve obtained in Example 3; Figure 10 The XRD pattern of the graded-pore Y-type molecular sieve obtained in Example 4; Figure 11 The N2 adsorption-desorption isotherm diagram of the graded pore Y-type molecular sieve obtained in Example 4; Figure 12 The XRD pattern of the graded-pore Y-type molecular sieve obtained in Example 5; Figure 13The N2 adsorption-desorption isotherm diagram of the graded-pore Y-type molecular sieve obtained in Example 5; Figure 14 The XRD pattern of the graded-pore Y-type molecular sieve obtained in Example 6; Figure 15 The N2 adsorption-desorption isotherm diagram of the graded pore Y-type molecular sieve obtained in Example 6; Figure 16 The XRD pattern of the graded-pore Y-type molecular sieve obtained in Example 7; Figure 17 The N2 adsorption-desorption isotherm diagram of the graded pore Y-type molecular sieve obtained in Example 7; Figure 18 The XRD pattern of the Y-type molecular sieve obtained in Comparative Example 1 is shown. Figure 19 The N2 adsorption-desorption isotherm of the Y-type molecular sieve obtained in Comparative Example 1; Figure 20 The image shows a scanning electron microscope (SEM) image of the Y-type molecular sieve obtained in Comparative Example 1. Figure 21 The XRD pattern of the Y-type molecular sieve obtained in Comparative Example 2 is shown. Figure 22 The N2 adsorption-desorption isotherm of the Y-type molecular sieve obtained in Comparative Example 2; Figure 23 The image shows a scanning electron microscope (SEM) image of the Y-type molecular sieve obtained in Comparative Example 2. Figure 24 The XRD pattern of the Y-type molecular sieve obtained in Comparative Example 3 is shown. Figure 25 The N2 adsorption-desorption isotherm of the Y-type molecular sieve obtained in Comparative Example 3; Figure 26 The image shows a scanning electron microscope (SEM) image of the Y-type molecular sieve obtained in Comparative Example 3. Figure 27 The XRD pattern of the Y-type molecular sieve obtained in Comparative Example 4 is shown. Figure 28 The N2 adsorption-desorption isotherm of the Y-type molecular sieve obtained in Comparative Example 4 is shown. Detailed Implementation

[0016] This invention provides a method for preparing graded-pore Y-type molecular sieves using rice husks as raw material, comprising the following steps: (1) Rice husks are subjected to pyrolysis and alkali activation to obtain activated rice husk char. The rice husks are pyrolyzed in an air atmosphere, then the pyrolyzed rice husks are mixed with an alkaline solution and dried, and then activated at high temperature in an inert atmosphere. The product is not washed after alkali activation to retain the alkaline substances and silicon species for subsequent molecular sieve synthesis.

[0017] (2) The activated rice husk char obtained in step (1) is mixed with deionized water and thoroughly mixed under heating and stirring conditions. After cooling, an aluminum source is added and stirring is continued to form a carbon-containing seed gel. The carbon-containing seed gel is then allowed to stand and age at room temperature to obtain a carbon-seed gel system.

[0018] (3) Add aluminum source and deionized water to the carbon-seed gel system obtained in step (2) to adjust the silicon-aluminum ratio of the synthesis system and obtain a mixture of molecular sieve precursor gel and rice husk carbon.

[0019] (4) The precursor gel obtained in step (3) is separated by filtration to remove the excess free liquid phase on the outer layer of rice husk carbon. Then the obtained wet material is transferred into a crystallization kettle for hydrothermal crystallization to obtain carbon-molecular sieve composite.

[0020] (5) The carbon-molecular sieve complex obtained in step (4) is filtered and washed until the filtrate is neutral, then dried and calcined to remove the rice husk carbon template to obtain graded pore Y-type molecular sieve.

[0021] In this invention, sodium hydroxide is preferably used as the alkali source for the alkali activation; the aluminum source can be selected from one or more of aluminum powder, sodium aluminate, aluminum hydroxide or aluminum sulfate.

[0022] In this invention, the preferred pyrolysis temperature of rice husks is 350-450°C. o C, Alkali activation is preferably performed under an inert atmosphere at 700-900°C. o C is carried out. The preferred molar ratio of each component in the carbon-containing seed gel is Na2O : Al2O3 : SiO2 : H2O = (15-20) : 1 : (15-25) : (300-450). The optimal aging time is 12-48 hours.

[0023] In this invention, the molecular sieve precursor gel ratio is Na₂O : Al₂O₃ : SiO₂ : H₂O = (4-16) : 1 : (8-16) : (120-900); the preferred hydrothermal crystallization temperature is 70-100 °C. o C, the crystallization time is preferably 12-36 hours.

[0024] This invention regulates the participation of rice husk-derived activated carbon in the molecular sieve synthesis process and controls the water content of the precursor system before crystallization, effectively adjusting the size and stacking mode of the molecular sieve crystals. While maintaining the stability of the Y-type molecular sieve crystal structure and crystallinity, it promotes the formation of intercrystalline mesopores and hierarchical pore structures.

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Example 1

[0026] Natural rice husks were heated in air at 400°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, where the mass ratio of NaOH to pyrolyzed rice husks was 1.17. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 3°C ​​under a nitrogen atmosphere. o Heating rate increased to 800 °C / min o Activation at C for 0.5 h yielded activated rice husk char. The activated rice husk char was then mixed with deionized water and heated at 80 °C. o The mixture was stirred at C for 5 h, cooled to room temperature, and then aluminum powder was added, with stirring continuing for 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum powder and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a mixture of black precursor gel and rice husk charcoal was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 7.58:1:8:540. The obtained precursor gel was filtered to remove excess mother liquor from the outer layer of rice husk charcoal, and the resulting wet material was then subjected to 80°C. o Hydrothermal crystallization at C for 12 h yielded a carbon-molecular sieve composite. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to hydrothermal treatment at 100 °C. o Dry at C, then at 550°C in air atmosphere. o The rice husk char template was removed by calcination at C for 4 h to obtain a hierarchical porous Y-type molecular sieve. The obtained hierarchical porous Y-type molecular sieve was characterized by nitrogen adsorption-desorption testing, and its pore structure parameters are as follows: specific surface area of ​​835 m² / g. 2 / g, with a microporous specific surface area of ​​793m² 2 / g, with an external specific surface area of ​​42 m² 2 / g, total pore volume is 0.53 cm³ 3 / g, external pore volume is 0.23 cm³ 3 / g. Example 2

[0027] Natural rice husks were heated in air at 400°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, where the mass ratio of NaOH to pyrolyzed rice husks was 1.17. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 3°C ​​under a nitrogen atmosphere. oHeating rate increased to 800 °C / min o Activation at C for 0.5 h yielded activated rice husk char. The activated rice husk char was then mixed with deionized water and heated at 80 °C. o The mixture was stirred at C for 5 h, cooled to room temperature, and then aluminum powder was added, with stirring continuing for 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum powder and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a mixture of black precursor gel and rice husk charcoal was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 11.4:1:12.0:600. The obtained precursor gel was filtered to remove excess free liquid phase from the outer layer of the rice husk charcoal. The resulting wet material was then subjected to 80°C. o Hydrothermal crystallization at C for 24 h yielded a carbon-molecular sieve composite. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to hydrothermal treatment at 100 °C. o Dry at C, then at 550°C in air atmosphere. o The rice husk char template was removed by calcination at C for 4 h to obtain a hierarchical porous Y-type molecular sieve. The obtained hierarchical porous Y-type molecular sieve was characterized by nitrogen adsorption-desorption testing, and its pore structure parameters are as follows: specific surface area of ​​815 m² / g. 2 / g, with a microporous specific surface area of ​​748 m² 2 / g, with an external specific surface area of ​​67 m² 2 / g, total pore volume is 0.68 cm³ 3 / g, external pore volume is 0.39 cm³ 3 / g. Example 3

[0028] Natural rice husks were heated in air at 400°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, where the mass ratio of NaOH to pyrolyzed rice husks was 1.17. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 3°C ​​under a nitrogen atmosphere. o Heating rate increased to 800 °C / min o Activation at C for 0.5 h yielded activated rice husk char. The activated rice husk char was then mixed with deionized water and heated at 80 °C. oThe mixture was stirred at C for 5 h, cooled to room temperature, and then aluminum powder was added and stirring continued for 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum powder and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a mixture of black precursor gel and rice husk charcoal was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 15.16:1:16:900. The obtained precursor gel was filtered to remove excess free liquid phase from the outer layer of the rice husk charcoal. The resulting wet material was then subjected to 80°C. o Hydrothermal crystallization at C conditions for 12 h yielded a carbon-molecular sieve composite. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to 100°C. o Dry at C, then in air at 550°C. o The rice husk char template was removed by calcination at C for 4 h to obtain a hierarchical porous Y-type molecular sieve. The obtained hierarchical porous Y-type molecular sieve was characterized by nitrogen adsorption-desorption testing, and its pore structure parameters are as follows: specific surface area of ​​802 m² / g. 2 / g, microporous specific surface area is 700 m² 2 / g, with an external specific surface area of ​​102 m² 2 / g, total pore volume is 1.21 cm³ 3 / g, external pore volume is 0.97 cm³ 3 / g. Example 4

[0029] Natural rice husks were heated in air at 450°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, where the mass ratio of NaOH to pyrolyzed rice husks was 1.2. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 3°C ​​under a nitrogen atmosphere. o Heating rate increased to 800 °C / min o Activation at C for 0.5 h yielded activated rice husk char. The activated rice husk char was then mixed with deionized water and heated at 80 °C. oThe mixture was stirred at C for 5 h, cooled to room temperature, and then sodium aluminate was added, followed by stirring for another 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 20:1:18:380. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum hydroxide and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a mixture of black precursor gel and rice husk charcoal was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 7.5:1:8:540. The obtained precursor gel was filtered to remove excess free liquid phase from the outer layer of the rice husk charcoal. The resulting wet material was then subjected to 90°C. o Hydrothermal crystallization at C for 12 h yielded a carbon-molecular sieve composite. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to hydrothermal treatment at 100 °C. o Dry at C, then at 550°C in air atmosphere. o Calcination at C for 4 h was performed to remove the rice husk carbon template, yielding a hierarchical Y-type molecular sieve with a specific surface area of ​​813 m². 2 / g, with a microporous specific surface area of ​​689 m² 2 / g, with an external specific surface area of ​​124 m² 2 / g, total pore volume is 0.73 cm³ 3 / g, external pore volume is 0.47cm³ 3 / g. Example 5

[0030] Natural rice husks were heated in air at 400°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, where the mass ratio of NaOH to pyrolyzed rice husks was 1.32. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 3°C ​​under a nitrogen atmosphere. o Heating rate increased to 800 °C / min o Activation at C for 0.5 h yielded activated rice husk char. The activated rice husk char was then mixed with deionized water and heated at 80 °C. oThe mixture was stirred at C for 5 h, cooled to room temperature, and then aluminum hydroxide was added, with stirring continued for 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum sulfate and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a mixture of black precursor gel and rice husk charcoal was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 7.5:1:8:510. The obtained precursor gel was filtered to remove excess free liquid phase from the outer layer of the rice husk charcoal. The resulting wet material was then subjected to 80°C. o Hydrothermal crystallization at C for 24 h yielded a carbon-molecular sieve composite. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to hydrothermal treatment at 100 °C. o Dry at C, then at 550°C in air atmosphere. o Calcination at C for 4 h was performed to remove the rice husk char template, yielding a hierarchical Y-type molecular sieve with a specific surface area of ​​792 m². 2 / g, with a microporous specific surface area of ​​660 m² 2 / g, with an external specific surface area of ​​132 m² 2 / g, total pore volume is 0.69 cm³ 3 / g, external pore volume is 0.43cm 3 / g. Example 6

[0031] Natural rice husks were heated in air at 350°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, where the mass ratio of NaOH to pyrolyzed rice husks was 1.25. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 5°C under a nitrogen atmosphere. o Heating rate increased to 850 °C / min o Activation at C for 0.5 h yielded activated rice husk char. The activated rice husk char was then mixed with deionized water and heated at 80 °C. oThe mixture was stirred at C for 5 h, cooled to room temperature, and then sodium aluminate was added, followed by stirring for another 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 20: 1: 19: 420. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum sulfate and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a mixture of black precursor gel and rice husk charcoal was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 7.8: 1: 8.2: 550. The obtained precursor gel was filtered to remove excess free liquid phase from the outer layer of the rice husk charcoal. The resulting wet material was then cooled at 85°C. o Hydrothermal crystallization at C for 12 h yielded a carbon-molecular sieve composite. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to hydrothermal treatment at 100 °C. o Dry at C, then at 550°C in air atmosphere. o Calcination at C for 4 h was performed to remove the rice husk char template, yielding a hierarchical Y-type molecular sieve with a specific surface area of ​​773 m². 2 / g, with a microporous specific surface area of ​​645 m² 2 / g, with an external specific surface area of ​​128 m² 2 / g, total pore volume is 0.67 cm³ 3 / g, external pore volume is 0.42cm³ 3 / g. Example 7

[0032] Natural rice husks were heated in air at 450°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, wherein the mass ratio of NaOH to pyrolyzed rice husks was 0.95. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 5°C under a nitrogen atmosphere. o Heating rate increased to 850 °C / min o Activation at C for 0.5 h yielded activated rice husk char. The activated rice husk char was then mixed with deionized water and heated at 80 °C. oThe mixture was stirred at C for 5 h, cooled to room temperature, and then sodium aluminate was added, followed by stirring for another 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 16:1:17:360. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum sulfate and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a mixture of black precursor gel and rice husk charcoal was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 7.1:1:7.8:530. The obtained precursor gel was filtered to remove excess free liquid phase from the outer layer of the rice husk charcoal. The resulting wet material was then subjected to 85°C. o Hydrothermal crystallization at C for 12 h yielded a carbon-molecular sieve composite. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to hydrothermal treatment at 100 °C. o Dry at C, then at 550°C in air atmosphere. o Calcination at C for 4 h was performed to remove the rice husk char template, yielding a hierarchical Y-type molecular sieve with a specific surface area of ​​766 m². 2 / g, with a microporous specific surface area of ​​636 m² 2 / g, with an external specific surface area of ​​130 m² 2 / g, total pore volume is 0.65 cm³ 3 / g, external pore volume is 0.40 cm³ 3 / g.

[0033] Comparative Example 1 Natural rice husks were heated in air at 800°C. o The rice husk ash was roasted at C for 1 h. The resulting rice husk ash was then dissolved in sodium hydroxide solution to obtain a sodium silicate solution. Aluminum powder was added to the sodium silicate solution and stirring was continued for 12 h, resulting in a final molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a seed gel. Aluminum powder and deionized water were added to the obtained seed gel system, and after stirring until homogeneous, a precursor gel was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 7.58:1:8:540. As a comparison, the obtained precursor gel was filtered to remove excess water, and the resulting wet material was aged at 80 °C. o Hydrothermal crystallization was carried out at C for 12 h. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to 100°C. o Dry at C, then at 550°C in air atmosphere. o C calcination for 4 h yielded Y-type molecular sieves. The obtained Y-type molecular sieves were characterized by nitrogen adsorption-desorption testing, and their pore structure parameters are as follows: specific surface area S... BET= 873 m 2 / g, with a microporous specific surface area of ​​842 m² 2 / g, with an external specific surface area of ​​31 m² 2 / g, total pore volume is 0.38 cm³ 3 / g, external pore volume is 0.06 cm³ 3 / g.

[0034] Comparative Example 2 Natural rice husks were heated in air at 800°C. o The rice husk ash was roasted at C for 1 h. The resulting rice husk ash was then dissolved in sodium hydroxide solution to obtain a sodium silicate solution. Aluminum powder was added to the sodium silicate solution and stirring was continued for 12 h, resulting in a final molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a seed gel. Aluminum powder and deionized water were added to the obtained seed gel system, and after stirring until homogeneous, a precursor gel was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 11.4:1:12.0:600. As a comparison, the obtained precursor gel was filtered to remove excess water, and the resulting wet material was aged at 80°C. o Hydrothermal crystallization was carried out at C for 24 h. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to 100°C. o Dry at C, then at 550°C in air atmosphere. o C calcination for 4 hours yielded Y-type molecular sieves. The obtained Y-type molecular sieves were characterized by nitrogen adsorption-desorption testing, and their pore structure parameters are as follows: specific surface area S... BET = 865 m 2 / g, with a microporous specific surface area of ​​836 m² 2 / g, with an external specific surface area of ​​29 m² 2 / g, total pore volume is 0.39 cm³ 3 / g, external pore volume is 0.07 cm³ 3 / g.

[0035] Comparative Example 3 Natural rice husks were heated in air at 800°C. oThe rice husk ash was roasted at C for 1 h. The resulting rice husk ash was then dissolved in sodium hydroxide solution to obtain a sodium silicate solution. Aluminum powder was added to the sodium silicate solution and stirring was continued for 12 h, resulting in a final molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a seed gel. Aluminum powder and deionized water were added to the obtained seed gel system, and after stirring until homogeneous, a precursor gel was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 15.16:1:16:900. As a comparison, the obtained precursor gel was filtered to remove excess water, and the resulting wet material was aged at 80 °C. o Hydrothermal crystallization was carried out at C for 12 h. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to 100°C. o Dry at C, then at 550°C in air atmosphere. o C calcination for 4 h yielded Y-type molecular sieve. The obtained Y-type molecular sieve was characterized by nitrogen adsorption-desorption testing, and its pore structure parameters are as follows: specific surface area of ​​881 m² / g. 2 / g, with a microporous specific surface area of ​​847 m² 2 / g, with an external specific surface area of ​​34 m² 2 / g, total pore volume is 0.37 cm³ 3 / g, external pore volume is 0.05 cm³ 3 / g.

[0036] Comparative Example 4 Natural rice husks were heated in air at 400°C. o Pyrolysis at C for 1 h. Then, the pyrolyzed rice husks were mixed with a 1 mol / L sodium hydroxide solution, where the mass ratio of NaOH to pyrolyzed rice husks was 1.17. The mixture was then heated at 100 °C. o Drying at C. The resulting mixture was ground and placed in a tube furnace, then dried at 3°C ​​under a nitrogen atmosphere. o Heating rate increased to 800 °C / min o Activated rice husk char was obtained by activating the rice husk char at 80°C for 0.5 h. The activated rice husk char was then mixed with deionized water and heated at 80°C. oAfter stirring at C for 5 h and cooling to room temperature, aluminum powder was added and stirring continued for 12 h to form a carbon-containing seed gel with a molar ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 18:1:19:370. The seed gel was then aged at room temperature for 24 h to obtain a carbon-seed gel system. Aluminum powder and deionized water were added to the obtained carbon-seed gel system, and after stirring until homogeneous, a black precursor gel was obtained with a gel ratio of Na₂O: Al₂O₃: SiO₂: H₂O = 7.58:1:8:540. For comparison, the obtained precursor gel was not filtered but directly subjected to 80 °C. o Hydrothermal crystallization was performed at C for 12 h. After crystallization, the resulting product was filtered, washed until neutral, and then subjected to hydrothermal treatment at 100 °C. o Dry at C, then at 550°C in air atmosphere. o C calcination for 4 h yielded Y-type molecular sieve. The obtained Y-type molecular sieve was characterized by nitrogen adsorption-desorption testing, and its pore structure parameters are as follows: specific surface area of ​​848 m² / g. 2 / g, with a microporous specific surface area of ​​821 m² 2 / g, with an external specific surface area of ​​27 m² 2 / g, total pore volume is 0.31 cm³ 3 / g, external pore volume is 0.03 cm³ 3 / g.

[0037] Characterization: Figure 1 , Figure 4 , Figure 7 , Figure 10 , Figure 12 , Figure 14 , Figure 16 , Figure 18 , Figure 21 , Figure 24 and Figure 27 The XRD patterns of each sample are shown. It can be seen that all samples exhibit the characteristic diffraction peaks of the FAU-structured Y-type molecular sieve, indicating that the obtained samples successfully formed a Y-type molecular sieve structure. Figure 2 , Figure 5 , Figure 8 , Figure 11 , Figure 13 , Figure 15 , Figure 17 , Figure 19 , Figure 22 , Figure 25 and Figure 28The N2 adsorption-desorption isotherms for each sample are shown. All samples exhibited a significant and rapid increase in adsorption capacity in the low relative pressure region, indicating that the samples all possess abundant microporous structures. Compared with the comparative samples, the example samples showed a more significant increase in adsorption capacity in the high relative pressure region (P / P0 > 0.9), indicating the presence of abundant intercrystalline mesopores and hierarchical pore structures in the samples. Among them, Example 3 showed the largest increase in adsorption capacity, corresponding to the highest total pore volume (1.21 cm³). 3 / g) and external pore volume (0.97 cm³) 3 / g). Figure 3 , Figure 6 , Figure 9 , Figure 20 , Figure 23 and Figure 26 The images show scanning electron microscope (SEM) images of some representative samples. As can be seen, the samples prepared via the activated rice husk char route consist of aggregates of small-sized nano-Y-type molecular sieve crystals, forming numerous intercrystalline channels. In contrast, the comparative samples exhibit larger single-crystal particles with diameters of approximately 0.8-1.5 μm, with denser packing and less abundant intercrystalline channels. Furthermore, Comparative Example 4, by eliminating the filtration step while maintaining the rice husk char system, reduced its external specific surface area and external pore volume to 27 m². 2 / g and 0.03 cm 3 / g, all significantly lower than 42 m in Example 1. 2 / g and 0.23 cm 3 / g indicates that pre-crystallization filtration to remove excess mother liquor can effectively inhibit excessive crystal growth and promote the formation of intercrystalline mesopores and hierarchical pore structures.

[0038] The above results indicate that by utilizing activated rice husk char as both a silicon source and a hard template, and combining it with a pre-crystallization filtration and water control strategy, this invention can effectively regulate the nucleation, growth, and grain stacking behavior of molecular sieves, thereby obtaining Y-type molecular sieves with high external specific surface area, large external pore volume, and well-developed hierarchical pore structure.

[0039] 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 graded-pore Y-type molecular sieves using rice husks as raw material, characterized in that, Includes the following steps: (1) Pyrolysis and NaOH activation treatment of rice husks to obtain activated rice husk char. The product is not washed after alkali activation in order to retain the alkaline substances and silicon species therein. (2) The activated rice husk char is mixed with water and an aluminum source to form a carbon-containing seed gel, and then aged to obtain a char-seed gel system; (3) Add aluminum source and water to the carbon-seed gel system to obtain a mixture of molecular sieve precursor gel and rice husk carbon; (4) The precursor gel is filtered to remove excess liquid phase on the outer layer of rice husk char, and then hydrothermal crystallization is performed to obtain char-molecular sieve complex. (5) The carbon-molecular sieve composite is washed, dried and calcined to remove the rice husk carbon template to obtain a graded pore Y-type molecular sieve.

2. The method for using graded-pore Y-type molecular sieves according to claim 1, characterized in that: The rice husk pyrolysis temperature in step (1) is 350-450°C. o The mass ratio of C, NaOH, and pyrolyzed rice husks is 0.8-1.

4. Alkali activation is performed under an inert atmosphere at 700-900 °C. o C proceeds.

3. The method for using graded-pore Y-type molecular sieves according to claim 1, characterized in that: The aluminum source mentioned in step (2) is one or more of aluminum powder, sodium aluminate, aluminum sulfate, and aluminum hydroxide. The molar ratio of the carbon seed gel is Na2O : Al2O3 : SiO2 : H2O = (15-20) : 1 : (15-25) : (300-450).

4. The method for using graded-pore Y-type molecular sieves according to claim 1, characterized in that: The aluminum source mentioned in step (3) is one or more of aluminum powder, sodium aluminate, aluminum sulfate, and aluminum hydroxide. The final ratio of the molecular sieve precursor gel is Na2O : Al2O3 : SiO2 : H2O = (4-16) : 1 : (8-16) : (120-900).

5. The method for using graded-pore Y-type molecular sieves according to claim 1, characterized in that: The filtration described in step (4) is performed before hydrothermal crystallization to reduce the content of free liquid phase in the outer layer of the precursor gel, thereby controlling the molecular sieve crystallization process. The hydrothermal crystallization temperature is 70-100°C. o C, crystallization time is 12-36 h.

6. The method for using graded-pore Y-type molecular sieves according to claim 1, characterized in that: The molecular sieve described in step (5) is formed by the aggregation of nano Y-type molecular sieve grains and has a hierarchical pore structure in which micropores and intercrystalline mesopores coexist.

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