Method for preparing zsm-5 molecular sieve by using industrial solid waste silica fume and application thereof

Abstract

The application discloses a method for preparing ZSM-5 molecular sieve by using industrial solid waste silica ash, and establishes an acid pickling-thermal activation combined pretreatment process, which can efficiently remove impurities and activate the silicon source without alkali fusion activation; the obtained activated silica ash is used as the only silicon source in the synthesis of the molecular sieve, and ZSM-5 molecular sieve is prepared under hydrothermal crystallization conditions; the method realizes precise regulation in a wide range of high-silicon-aluminum ratio 1:100-1:800, all the products maintain pure-phase MFI structure, the BET specific surface area is above 350 m 2 / g, the total pore volume reaches 0.14-0.16 cm 3 / g, and a micro-mesoporous composite structure with a pore size concentrated in 2-5 nm is spontaneously formed; the prepared ZSM-5 molecular sieve can be used as an oxygen carrier framework of a chemical looping reaction. The application does not need to add seeds, special templates or pore expanding agents, has a simple process flow and low cost, realizes high-value utilization of the silica ash, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to a method and application for preparing ZSM-5 molecular sieves using industrial solid waste silica fume, belonging to the fields of solid waste resource utilization and zeolite molecular sieve synthesis and application. Background Technology

[0002] ZSM-5 molecular sieves are widely used in petroleum cracking, fine chemicals, and environmental protection due to their unique shape-selective catalytic properties and good thermal stability. Traditional synthesis of ZSM-5 molecular sieves mainly relies on hydrothermal crystallization, using high-purity chemical reagents such as silica sol, water glass, and sodium aluminate as raw materials. This method suffers from high cost, complex processes, and significant environmental pollution. Therefore, utilizing industrial solid waste to replace traditional silicon and aluminum sources, achieving high-value utilization of solid waste resources, has become an important research direction in this field.

[0003] In recent years, researchers have made some progress in synthesizing ZSM-5 molecular sieves using industrial solid wastes such as fly ash, alumina ash, and kaolin. For example, CN111333081B discloses a method for preparing low-silicon-alumina ratio ZSM-5 using high-alumina pulverized coal furnace fly ash as raw material, but the silicon-alumina ratio of the product is only 12.62, which is difficult to meet the application requirements of high silicon-alumina ratio. Although CN113896207B and CN118005037A have achieved the synthesis of higher silicon-alumina ratios, they rely on seed crystal guidance, and the process flow is relatively complex. CN117049564A and CN120136127A respectively used special template agents and biomass pore expanders to achieve the construction of hierarchical pore structures, but the introduction of additional additives increased the raw material cost. CN119038574A attempted to synthesize ZSM-5 using microsilica powder as raw material, but its pretreatment only involved simple water washing, which failed to effectively remove impurities and activate the silicon source activity, and it did not achieve a wide range of control over the silicon-to-aluminum ratio, resulting in a product with a simple pore structure.

[0004] Meanwhile, Chemical Looping Technology (CLT), as a novel reaction technology enabling efficient energy conversion and chemical synthesis, has attracted widespread attention in recent years. This technology breaks down traditional reactions into multiple sub-reactions through the circulation of oxygen carriers (or nitrogen carriers, carbon carriers) between reactors, thereby achieving energy cascade utilization and in-situ product separation. The oxygen carrier is the core of CLT, typically composed of active metal oxides (such as Fe₂O₃, CuO, NiO, Mn₂O₃, etc.) supported on a porous framework material. However, during high-temperature (typically >800℃) redox cycles, metal oxides are prone to severe sintering and agglomeration, leading to decreased oxygen carrier activity and poor cycle stability, severely hindering the industrial application of CLT. Loading the active component onto a framework material with high thermal stability and a regular porous structure is an effective strategy to inhibit sintering and improve dispersibility. An ideal oxygen carrier framework should possess the following characteristics: (1) high thermal stability, capable of withstanding repeated oxidation-reduction cycles above 800℃; (2) high specific surface area, which is beneficial for the high dispersion of active components; and (3) suitable pore structure, which can both anchor metal oxide particles and inhibit their migration and aggregation, and facilitate the diffusion and mass transfer of reactant gases. ZSM-5 molecular sieves, due to their regular pore structure and good thermal stability, theoretically have the potential to serve as an oxygen carrier framework, but the traditional synthesis cost is high, and there are no reports on the systematic research and application of it as an oxygen carrier framework.

[0005] Silica ash is a major solid waste generated during the production of metallic silicon. It is rich in amorphous SiO2 (content can reach over 90%) and is a potential high-quality silicon source. However, the technology for high-value utilization of silica ash is still immature, and existing methods have not fully realized its potential, especially in the development of high-performance molecular sieve materials that can serve as oxygen carrier frameworks for chemical chain reactions, which remains a gap. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing ZSM-5 molecular sieves using industrial solid waste silica fume. This method establishes a combined "acid washing-thermal activation" pretreatment process tailored to the characteristics of silica fume, efficiently removing impurities and activating the silicon source without the need for alkaline fusion activation. The resulting activated silica fume serves as the sole silicon source in the molecular sieve synthesis. Furthermore, by precisely controlling the amount of aluminum source added, a wide range of silicon-to-aluminum ratio (1:100~1:800) can be achieved. Under suitable hydrothermal crystallization conditions, pure-phase, highly crystalline ZSM-5 molecular sieves are prepared. Within this wide range, the products maintain a pure-phase MFI structure, and the BET specific surface area remains stable at 350 m². 2 / g or more, with a total pore volume of 0.14-0.16 cm³. 3 / g, and spontaneously formed a micro-mesoporous composite structure with pore sizes concentrated in the 2-5nm range. Thermogravimetric analysis showed that the obtained molecular sieve maintained a stable framework structure at 800℃, fully meeting the requirements for thermal stability, specific surface area, and pore structure as an oxygen carrier framework for chemical looping reactions. This invention requires no addition of seed crystals, special template agents, or pore expanders, and the process is simple and low-cost, providing a new technical solution for the high-value utilization of silica fume, while also providing a high-performance, low-cost oxygen carrier framework material for chemical looping reaction technology.

[0007] Another objective of this invention is to apply the aforementioned ZSM-5 molecular sieve as an oxygen carrier framework in chemical chain reactions.

[0008] The method for preparing ZSM-5 molecular sieves using industrial solid waste silica fume is as follows: (1) Add silica fume to a 1-3 mol / L acid solution at a solid-liquid ratio of 1:3-1:6 g:mL and stir in a 30-60℃ water bath for 2-6 hours for acid washing; after acid washing, filter with deionized water until neutral, dry and calcine the silica fume after washing, and grind it to obtain activated silica fume. The calcination activation temperature is 500-600℃, and the time is 1-3 hours; the acid is hydrochloric acid, sulfuric acid, or nitric acid. (2) Mix activated silica fume, aluminum source, alkali source, template agent and water. Place the mixture in a water bath at 60-90℃ and stir for 2-6 hours. Then let it stand for aging for 10-14 hours. Pour the aging product into a reaction vessel and crystallize it at 140-170℃ for 48-96 hours. Then filter and wash it with deionized water until it is neutral. Dry and calcine the filter cake to obtain ZSM-5 molecular sieve. The aluminum source is one or more of aluminum nitrate nonahydrate, aluminum sulfate, and sodium aluminate; the alkali source is sodium hydroxide or potassium hydroxide; the template agent is tetrapropylammonium hydroxide; based on SiO2 in activated silica fume, the amount of aluminum salt is converted to Al2O3; the molar ratio of SiO2 to Al2O3 is 1:0.00125-0.01; the molar ratio of SiO2 to alkali source is 1:0.2-0.3; the molar ratio of SiO2 to template agent is 1:0.2-0.3; and the molar ratio of SiO2 to H2O is 1:15-25.

[0009] The roasting process involves treating the food at 500-600℃ for 6-8 hours.

[0010] The ZSM-5 molecular sieve prepared by this invention has the following structural features, making it particularly suitable as a framework material for oxygen carriers in chemical chain reactions: (1) High thermal stability: Thermogravimetric analysis shows that the material’s skeleton structure remains stable at 800℃ and can withstand the high temperature environment associated with repeated oxidation-reduction cycles during the chemical chain reaction process; (2) High specific surface area: The specific surface area of ​​BET is stable at 350m². 2 With a concentration of over / g, sufficient loading sites can be provided for the active components of metal oxides, achieving high dispersion and thus improving the utilization rate of the active components; (3) Micro-mesoporous composite structure: The product spontaneously forms mesopores with a pore size concentrated in 2-5 nm, which together with the intrinsic micropores of the molecular sieve constitute a multi-level pore system. This structure can both use mesopores to anchor metal oxide particles and suppress their migration and aggregation during high-temperature cycling through confinement effect, and use micropores to ensure the diffusion and mass transfer of reactant gas and product gas, thereby reducing mass transfer resistance. (4) Adjustable silicon-aluminum ratio: For the first time, the silicon-aluminum ratio can be precisely controlled over a wide range from 100 to 800, which makes the acidity and hydrophilicity / hydrophobicity of the framework adjustable. It can adapt to the loading requirements of different metal oxide active components (such as Fe2O3, CuO, NiO, Mn2O3, Co3O4, etc.) and expand its application potential in various chemical chain reaction systems.

[0011] Based on the above characteristics, when the ZSM-5 molecular sieve prepared by this invention is used as a framework for oxygen carriers in chemical chain reactions, the following technical effects can be achieved: (1) Suppressing active component sintering: Through the channel confinement effect, it effectively prevents the migration and aggregation of the loaded metal oxide in the high-temperature oxidation-reduction cycle, and significantly improves the cycle life of the oxygen carrier; (2) Enhanced dispersibility of active components: High specific surface area provides sufficient anchoring points for active components, improving the reactivity of oxygen carrier per unit mass; (3) Maintaining the stability of the pore structure: Thermogravimetric analysis confirmed that its skeleton structure is stable at high temperature, ensuring that it maintains good gas diffusion channels after multiple switching of oxidation-reduction atmosphere, and avoiding the decrease in activity caused by pore collapse; (4) Outstanding cost advantage: Using industrial solid waste silica fume as raw material, the preparation cost of oxygen carrier skeleton is greatly reduced, providing an economical and feasible technical solution for the large-scale application of chemical chain reaction technology; (5) This invention does not require the addition of seed crystals, special template agents or pore expanders. Compared with existing technologies (such as CN113896207B, CN118005037A which rely on seed crystal guidance, CN117049564A which relies on special template agents, and CN120136127A which relies on biomass pore expanders), the process is significantly simplified and the raw material cost is greatly reduced, which has good prospects for industrial application.

[0012] This invention effectively solves the technical problem of silica fume solid waste disposal, providing a new solution for the high-value utilization of industrial solid waste silica fume. The raw materials used in this invention are widely available and inexpensive; the synthesis process is simple and easy to carry out industrially, with low energy consumption. Attached Figure Description

[0013] Figure 1 The XRD patterns of ZSM-5 molecular sieves in Examples 1-4 are shown. Figure 2 This is a pore size distribution diagram of the ZSM-5 molecular sieve in Example 1; Figure 3 This is a pore size distribution diagram of the ZSM-5 molecular sieve in Example 2; Figure 4 This is a pore size distribution diagram of the ZSM-5 molecular sieve in Example 3; Figure 5 This is a pore size distribution diagram of the ZSM-5 molecular sieve in Example 4; Figure 6 Thermogravimetric analysis spectrum of ZSM-5 molecular sieve. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the content described.

[0015] The silica ash used in the examples is derived from industrial solid waste generated during the production of metallic silicon. Its main component is amorphous SiO2 with a content of ≥90 wt%, and the remainder is a small amount of metal oxide impurities.

[0016] The reagents used in the examples were: hydrochloric acid (analytical grade), sodium hydroxide (analytical grade), aluminum nitrate nonahydrate (analytical grade), tetrapropylammonium hydroxide (analytical grade, 25 wt.% aqueous solution), and deionized water was prepared in the laboratory. Example 1

[0017] Silica fume was added to 2 mol / L hydrochloric acid at a solid-liquid ratio of 1:4 g:mL and stirred in a 40℃ water bath for 4 hours for acid washing. After acid washing, it was filtered with deionized water until neutral. Then, the washed silica fume was placed in a constant temperature drying oven and dried at 100℃ for 12 hours. The dried silica fume was then placed in a muffle furnace and calcined at 550℃ for 2 hours. After grinding, activated silica fume was obtained. Activated silica fume, aluminum nitrate nonahydrate, sodium hydroxide, template agent, and water were mixed. The amount of activated silica fume was calculated based on its SiO2 content, and the amount of aluminum nitrate nonahydrate was converted to Al2O3. The molar ratio of SiO2:Al2O3:NaOH:tetrapropylammonium hydroxide:H2O was 1:0.01:0.2:0.2:20. The mixed solution was stirred in an 80℃ water bath for 4 hours, and then allowed to stand for aging for 12 hours. The aged gel mixture was poured into a reaction vessel and crystallized at a constant temperature of 150℃ for 72 hours. After crystallization, the mixture was filtered and washed with deionized water until neutral. The filter cake was dried in a 100℃ oven for 12 hours. The dried sample was calcined in a muffle furnace at 550℃ for 6 hours to remove the template agent, thus obtaining the ZSM-5 molecular sieve product. The product was characterized by XRD, BET, and TG. The results are shown in the figure. Figure 1 , 2 And Table 1, XRD patterns of the products ( Figure 1 The sample exhibits typical ZSM-5 characteristic diffraction peaks, indicating that it possesses a ZSM-5 crystal structure. Pore size analysis ( Figure 2 The results (approximately 5.1 Å) are consistent with the inherent micropore size of ZSM-5. Furthermore, BET test results (Table 1) show that this material has a high specific surface area (334.4021 m²). 2 / g) and total pore volume (0.136783 cm³) 3 / g); Table 1. Specific surface area and total pore volume of ZSM-5 molecular sieves prepared from silica fume. . Example 2

[0018] The method used in this embodiment is the same as in Example 1, except that the molar ratio of SiO2 to Al2O3 is 1:0.003. The product was characterized using XRD, BET, and TG, and the results are shown below. Figure 1 , 3 And Table 1, XRD patterns of the products ( Figure 1 The sample exhibits typical ZSM-5 characteristic diffraction peaks, indicating that it possesses a ZSM-5 crystal structure. Pore size analysis ( Figure 3 The results (approximately 5.3 Å) are consistent with the inherent micropore size of ZSM-5. Furthermore, BET test results (Table 1) show that this material has a high specific surface area (358.8564 m²). 2 / g) and total pore volume (0.147564 cm³) 3 / g). Example 3

[0019] The method used in this embodiment is the same as in Example 1, except that the molar ratio of SiO2 to Al2O3 is 1:0.002. The product was characterized using XRD, BET, and TG, and the results are shown below. Figure 1 , 4 And Table 1, XRD patterns of the products ( Figure 1 The sample exhibits typical ZSM-5 characteristic diffraction peaks, indicating that it possesses a ZSM-5 crystal structure. Pore size analysis ( Figure 4 The results (approximately 5.2 Å) are consistent with the inherent micropore size of ZSM-5. Furthermore, BET test results (Table 1) show that this material has a high specific surface area (361.9024 m²). 2 / g) and total pore volume (0.148586 cm³) 3 / g). Example 4

[0020] The method used in this embodiment is the same as in Example 1, except that the molar ratio of SiO2 to Al2O3 is 1:0.00125. The product was characterized using XRD, BET, and TG, and the results are shown below. Figure 1 , 5 And Table 1, XRD patterns of the products ( Figure 1 The sample exhibits typical ZSM-5 characteristic diffraction peaks, indicating that it possesses a ZSM-5 crystal structure. Pore size analysis ( Figure 5 The results (approximately 5.3 Å) are consistent with the inherent micropore size of ZSM-5. Furthermore, BET test results (Table 1) show that this material has a high specific surface area (383.5786 m²). 2 / g) and total pore volume (0.156836 cm³) 3 / g).

[0021] To evaluate the feasibility of the ZSM-5 molecular sieve prepared in this invention as a framework for oxygen carriers in chemical looping combustion, thermogravimetric analysis was performed on the samples prepared in Examples 1-4. The results of Example 1 are as follows: Figure 6 As shown, the test conditions were air atmosphere, heating rate 10℃ / min, and temperature range from room temperature to 800℃. Examples 2, 3, and 4 showed the same results.

[0022] from Figure 6 It is evident that the weight loss of the samples mainly occurred in the range of room temperature to 400℃, with a weight loss rate of approximately 12-14%, which can be attributed to the removal of physically adsorbed water and the oxidative decomposition of residual template agent. When the temperature rises above 400℃, the thermogravimetric curve tends to be horizontal, and the weight loss rate in the 400-800℃ range is less than 2%, indicating that the molecular sieve framework remains stable at high temperatures without significant structural collapse or further weight loss.

[0023] Thermogravimetric analysis results confirm that the ZSM-5 molecular sieve prepared in this invention exhibits good structural stability at 800℃, and can withstand the high-temperature environment associated with repeated oxidation-reduction cycles during chemical looping combustion. Combined with BET characterization results (specific surface area >350 m²), 2 / g, total pore volume 0.14-0.16cm³ 3 / g, with pore sizes concentrated in the range of 2-5nm), this material possesses ideal characteristics as an oxygen carrier framework: high specific surface area facilitates the dispersion of active components, the micro-mesoporous composite structure can effectively anchor metal oxide particles and inhibit their sintering, and high-temperature stability ensures the structural integrity of the framework during cycling.

[0024] In summary, the ZSM-5 molecular sieve prepared by this invention fully meets the requirements of chemical looping combustion oxygen carrier framework for material thermal stability, pore structure and specific surface area, showing good application prospects as a high-performance oxygen carrier framework.

Claims

1. A method for preparing ZSM-5 molecular sieves using industrial solid waste silica fume, characterized in that: Add silica fume to a 1-3 mol / L acid solution at a solid-liquid ratio of 1:3-6 g:mL, and stir in a 30-60℃ water bath for 2-6 hours for acid washing. After acid washing, filter with deionized water until neutral, dry and calcine the silica fume, and grind it to obtain activated silica fume. Mix activated silica fume, aluminum source, alkali source, template agent and water. Place the mixture in a water bath at 60-90℃ and stir for 2-6 hours. Then let it stand for aging for 10-14 hours. Pour the aging product into a reaction vessel and crystallize at 140-170℃ for 48-96 hours. After filtration and washing with deionized water until neutral, dry and calcine the filter cake to obtain ZSM-5 molecular sieve.

2. The method for preparing ZSM-5 molecular sieve using industrial solid waste silica fume as described in claim 1, characterized in that: The acid is hydrochloric acid, sulfuric acid, or nitric acid; the aluminum source is one or more of aluminum nitrate nonahydrate, aluminum sulfate, and sodium aluminate; the alkali source is sodium hydroxide or potassium hydroxide; and the template agent is tetrapropylammonium hydroxide.

3. The method for preparing ZSM-5 molecular sieve using industrial solid waste silica fume according to claim 2, characterized in that: The activated silica fume is calculated as SiO2, the aluminum salt is calculated as Al2O3, the molar ratio of SiO2:Al2O3 is 1:0.00125-0.01, the molar ratio of SiO2:alkali source is 1:0.2-0.3, the molar ratio of SiO2:template agent is 1:0.2-0.3, and the molar ratio of SiO2:H2O is 1:15-25.

4. The application of ZSM-5 molecular sieve prepared by the method of preparing ZSM-5 molecular sieve using industrial solid waste silica fume as described in any one of claims 1-3 as an oxygen carrier framework in chemical chain reaction.

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