Method for preparing A-type fly ash-based molecular sieve by using dynamic self-adjusting hydrothermal method

Abstract

The invention discloses a method for preparing an A-type fly ash-based molecular sieve by using a dynamic self-adjusting hydrothermal method. The method comprises the following steps: step 1, pretreating a fly ash raw material; step 2, preparing an alkali solution; 3, mixing the pretreated fly ash with an alkali solution, and carrying out an alkali dissolution reaction; step 4, carrying out online analysis on the alkali dissolution reaction solution, and dynamically and adaptively adjusting the silicon-aluminum dissolution rate in the alkali dissolution process; step 5, aging reaction; step 6, crystallization reaction; step 7, carrying out online analysis on the crystallization reaction liquid, and dynamically and adaptively adjusting the crystallization process; 8, judging whether the crystallization reaction is finished or not, if not, returning to the step 6, and if so, executing the step 9; and 9, separating, washing and drying to obtain the A-type fly ash-based molecular sieve product. The method has the beneficial effects of simple operation and low cost; the product quality is high; the method is environment-friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve preparation, and particularly to a method for preparing A-type fly ash-based molecular sieve by dynamic self-regulating hydrothermal method. Background Art

[0002] As the main solid waste of thermal power plants, fly ash is produced in extremely large quantities every year. According to statistics, the annual fly ash emissions in China reach hundreds of millions of tons. It not only occupies a large amount of land resources, but also causes serious pollution to soil, water bodies and atmospheric environment after long-term accumulation. However, fly ash contains a large amount of components such as silicon dioxide and alumina, which are highly similar to the main components of molecular sieves. As a kind of aluminosilicate crystal with uniform microporous structure, molecular sieves have a wide range of applications in many fields such as petrochemical industry, environmental protection, gas separation, etc. Preparing fly ash into molecular sieves can not only realize the resource utilization of fly ash, reduce the environmental pressure caused by it, but also bring significant economic benefits, and has important research value and application prospects.

[0003] At present, a variety of technologies have been disclosed for preparing molecular sieves from fly ash, but these methods generally have many defects. The traditional hydrothermal synthesis technology uses a large amount of water as a solvent, which not only consumes a large amount of water resources, but also has a low product yield during the reaction process, usually difficult to exceed a certain proportion. The impure crystal form leads to unstable product performance, and the low crystallinity also limits its application in some high-end fields. In addition, after the crystallization is completed, a large amount of clean water is needed to wash the product, and these washing wastewaters contain high-concentration alkaline substances, and direct discharge will cause serious alkaline pollution to the environment, increasing the cost and difficulty of subsequent sewage treatment.

[0004] In the existing technologies for preparing A-type molecular sieves, the pretreatment and aging reactions often take a long time. The complex pretreatment steps not only increase the operation complexity, but also prolong the entire production cycle. The long-term aging reaction not only consumes a large amount of energy, but also significantly increases the production cost, reducing the competitiveness of the product in the market.

[0005] To solve these problems, researchers have conducted a large number of studies and achieved some results. For example, Patent CN115385356A discloses a method for preparing 13X zeolite using solid-phase fly ash. This method uses solid waste fly ash as raw material, which has a wide source and effectively reduces the environmental pollution caused by fly ash. At the same time, the solid-phase synthesis method is adopted to avoid the generation of a large amount of wastewater during the synthesis of zeolite. However, this method has deficiencies in the purity and cost control of zeolite and cannot meet the market demand for high-quality and low-cost zeolite products. Patent CN111533135A discloses a method for preparing A-type fly ash-based zeolite by dynamic self-regulating hydrothermal method. This method can use medium-aluminum or low-aluminum fly ash as raw material, dissolve it with NaOH by adding, recycle the fly ash crystallization filtrate, and combine pretreatment means such as ball milling, screening, and drying, and proportion the ingredients according to a certain ratio. With the help of automatic sampling online analysis and self-optimization method, dynamically and adaptively adjust the silicon-aluminum dissolution rate of the alkali dissolution process. After aging, further dynamically and adaptively adjust the crystallization process to ensure the crystal form and productivity. However, there is still room for improvement in the optimization of alkali dissolution and aging conditions, and further improvement is needed to improve product quality and production efficiency.

[0006] In summary, it is of urgent practical significance to develop a new method for preparing A-type fly ash-based zeolite with low energy consumption, low pollution, and simple operation for realizing the high-value utilization of fly ash and promoting the sustainable development of the zeolite industry. Summary of the Invention

[0007] To solve the above problems, especially aiming at the deficiencies of the existing technology, the present invention provides a method for preparing A-type fly ash-based zeolite by dynamic self-regulating hydrothermal method, which can solve the above problems.

[0008] To achieve the above object, the present invention adopts the following technical means:

[0009] A method for preparing A-type fly ash-based zeolite by dynamic self-regulating hydrothermal method, comprising the following steps:

[0010] Step 1, pretreat the fly ash raw material;

[0011] Step 2, prepare an alkali solution;

[0012] Step 3, mix the pretreated fly ash with the alkali solution and carry out an alkali dissolution reaction;

[0013] Step 4, conduct an online analysis of the alkali dissolution reaction solution and dynamically and adaptively adjust the silicon-aluminum dissolution rate of the alkali dissolution process;

[0014] Step 5, carry out an aging reaction;

[0015] Step 6, carry out a crystallization reaction;

[0016] Step 7: Conduct on-line analysis of the crystallization reaction solution and dynamically and adaptively adjust the crystallization process;

[0017] Step 8: Determine whether the crystallization reaction is completed. If not, return to Step 6. If completed, execute Step 9;

[0018] Step 9: Separate, wash, and dry to obtain the A-type fly ash-based molecular sieve product.

[0019] A further solution of the present invention is that in Step 1, the specific method for pretreating the fly ash raw material is as follows:

[0020] Step 101: Weigh the fly ash raw powder and dry it at 100 °C until constant weight;

[0021] Step 102: Mix the dried fly ash with a hydrochloric acid solution with a mass percentage concentration of 20% at a solid-liquid ratio of 1:20, and magnetically stir at 80 °C for 12 hours;

[0022] Step 103: Centrifuge at a centrifugal speed of 4000 rpm for 40 minutes, wash the filter cake with deionized water to remove the residual hydrochloric acid until the pH of the washing solution is 7, and dry the filter cake for standby.

[0023] A further solution of the present invention is that in Step 2, the alkali solution is a NaOH solution with a mass percentage concentration of 10% - 15%.

[0024] A further solution of the present invention is that in Step 3, the pretreated fly ash and the NaOH solution are mixed at a solid-liquid ratio of 1:4 - 5.

[0025] A further solution of the present invention is that in Step 4, by on-line analyzing the silicon-aluminum concentration of the alkali dissolution reaction solution, dynamically adjust the concentration and temperature of the NaOH solution, control the silicon-aluminum dissolution rate, and ensure that the silicon-aluminum ratio is within a suitable range.

[0026] A further solution of the present invention is that in Step 5, the aging temperature is 60 - 90 °C and the aging time is 4 - 12 hours.

[0027] A further solution of the present invention is that in Step 6, the crystallization temperature is 80 - 120 °C and the crystallization time is 4 - 12 hours.

[0028] A further solution of the present invention is that in Step 7, by on-line analyzing the silicon-aluminum concentration and pH value of the crystallization reaction solution, dynamically adjust the concentration and temperature of the NaOH solution to control the crystallization process.

[0029] A further solution of the present invention is that in step 7, by online analyzing the silicon-aluminum concentration and pH value of the crystallization reaction solution, when the pH value is lower than 12, NaOH solution is added to maintain the pH value at 12-13; when the silicon-aluminum ratio is lower than 1.6, the reaction temperature is increased to 110-120 °C to control the crystallization process.

[0030] A further solution of the present invention is that in step 9, the separation is carried out by centrifugal separation or filtration separation, the washing is carried out with deionized water, and the drying temperature is 100-120 °C.

[0031] Advantages of the present invention:

[0032] 1. The operation of the present invention is simple and the cost is low.

[0033] Simplified process: The present invention abandons the complex pretreatment and long-time aging reaction links in the traditional method, greatly shortens the process flow, and reduces the time and resource consumption brought by intermediate steps.

[0034] Reduced costs and energy consumption: By reducing the operation time and process complexity, the energy consumption, labor, equipment and other costs in the production process are correspondingly reduced, improving the economic benefits.

[0035] 2. The product quality of the present invention is high.

[0036] Real-time monitoring and optimization: Through the dynamic self-regulation technology, during the alkali dissolution and crystallization processes, the key parameters such as the silicon-aluminum concentration and pH value of the reaction solution are analyzed online in real time, and the concentration and temperature of the NaOH solution are dynamically adjusted accordingly to precisely control the reaction process.

[0037] Guaranteed product quality: The above operations ensure that the product has high purity and crystallinity, significantly improving the product quality. At the same time, the stable and high-quality product also improves the production efficiency and meets the market demand for high-quality molecular sieves.

[0038] 3. The present invention is environmentally friendly.

[0039] Reduced wastewater discharge: The present invention adopts the method of recycling the crystallization filtrate, greatly reducing the amount of fresh water used, thereby reducing the amount of wastewater generated, alleviating the environmental pollution pressure, and at the same time reducing the wastewater treatment cost.

[0040] High-value utilization of resources: Using fly ash, a solid waste, as the raw material to prepare molecular sieves realizes the resource utilization of waste, turning waste into treasure, reducing the harm of fly ash to the environment, and creating economic value, meeting the requirements of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the process flow chart of the present invention. Detailed implementation manners

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] Embodiment 1

[0044] As Figure 1 shown, a method for preparing A-type fly ash-based molecular sieve by dynamic self-regulating hydrothermal method includes the following steps:

[0045] Step 1: Pretreat the fly ash raw material;

[0046] Step 2: Prepare an alkali solution;

[0047] Step 3: Mix the pretreated fly ash with the alkali solution and carry out an alkali dissolution reaction;

[0048] Step 4: Conduct on-line analysis of the alkali dissolution reaction solution and dynamically and adaptively adjust the silicon-aluminum dissolution rate of the alkali dissolution process;

[0049] Step 5: Aging reaction;

[0050] Step 6: Crystallization reaction;

[0051] Step 7: Conduct on-line analysis of the crystallization reaction solution and dynamically and adaptively adjust the crystallization process;

[0052] Step 8: Judge whether the crystallization reaction is completed. If not, return to Step 6. If completed, execute Step 9;

[0053] Step 9: Separate, wash, and dry to obtain an A-type fly ash-based molecular sieve product.

[0054] In Step 1, the specific method for pretreating the fly ash raw material is as follows:

[0055] Step 101: Weigh the fly ash raw powder and dry it at 100 °C until constant weight;

[0056] Step 102: Mix the dried fly ash with a hydrochloric acid solution with a mass percentage concentration of 20% at a solid-liquid ratio of 1:20, and magnetically stir at 80 °C for 12 hours;

[0057] Step 103: Centrifuge and separate at a centrifugal speed of 4000 rpm for 40 minutes, wash the filter cake with deionized water to remove residual hydrochloric acid until the pH of the washing solution is 7, and dry the filter cake for standby.

[0058] The advantages of the above settings are as follows:

[0059] Improve the stability of raw materials:

[0060] Remove moisture: In step 101, the raw fly ash powder is dried at 100 °C until constant weight, effectively removing the moisture in the fly ash. The presence of moisture may affect the subsequent reaction, leading to instability of the reaction system. After removing the moisture, the consistency and stability of the subsequent reaction can be ensured, and the repeatability of the experiment can be improved.

[0061] Optimize the composition:

[0062] Remove impurities: In step 102, the dried fly ash is mixed with a hydrochloric acid solution with a mass percentage concentration of 20% at a ratio of 1:20 and magnetically stirred at 80 °C for 12 hours. This process enables some impurities in the fly ash to react with hydrochloric acid and be dissolved and removed. By removing these impurities, the relative content of silicon and aluminum components in the fly ash can be increased, providing a purer raw material for the subsequent preparation of molecular sieves and helping to improve the purity and performance of the molecular sieves.

[0063] Adjust the silicon-aluminum ratio: Through acid leaching treatment, the existence form and ratio of silicon and aluminum in the fly ash can also be appropriately adjusted to make it closer to the silicon-aluminum ratio required for the preparation of type A molecular sieves, which is beneficial to the subsequent reaction and improves the product quality.

[0064] Facilitate separation and purification:

[0065] Achieve solid-liquid separation: In step 103, centrifugal separation is carried out at a centrifugal speed of 4000 rpm for 40 minutes, which can effectively achieve rapid separation of the solid and liquid after acid leaching. Compared with other separation methods, centrifugal separation has high efficiency, can shorten the operation time, and can better collect the solid product, reducing product loss.

[0066] Ensure the purity of the product: Wash the filter cake with deionized water until the pH of the washing liquid is 7, which can completely remove the residual hydrochloric acid on the surface of the filter cake, prevent the residual hydrochloric acid from interfering with the subsequent reaction, ensure the purity of the subsequent reaction system, and thus lay a foundation for the preparation of high-purity type A fly ash-based molecular sieves.

[0067] Guarantee subsequent operations:

[0068] Provide dry raw materials: Finally, dry the filter cake for later use, providing dry raw materials for subsequent reactions such as alkali dissolution, avoiding the adverse effects of moisture on the alkali dissolution reaction, ensuring the smooth progress of the reaction, and at the same time facilitating the storage and transportation of raw materials.

[0069] In step 2, the alkali solution is a NaOH solution with a mass percentage concentration of 10% - 15%.

[0070] The advantages of the above settings are:

[0071] Effectively initiate and promote the reaction

[0072] Activating the activity of fly ash: NaOH can react with silicon dioxide and alumina in fly ash, destroying the original crystal structure of fly ash, promoting the dissolution of silicate and releasing active silicon-aluminum species. Controlling the concentration of the NaOH solution at 10%-15% can provide sufficient hydroxide ions for the reaction, smoothly initiate the reaction, ensure the smooth dissolution of the silicon-aluminum components in fly ash, and lay a material foundation for the subsequent formation of the molecular sieve structure.

[0073] Maintaining the continuous progress of the reaction: This concentration range can continuously provide a stable alkaline environment during the reaction process, avoid insufficient reaction driving force caused by too low alkali concentration and the reaction stagnating halfway, and ensure the smooth progress of subsequent reactions such as alkali dissolution and crystallization.

[0074] Precisely regulating the reaction process

[0075] Optimizing the dissolution rate of silicon and aluminum: The concentration of the 10%-15% NaOH solution can keep the dissolution rate of silicon and aluminum within a suitable range during the alkali dissolution process. By cooperating with on-line analysis and dynamic regulation means, the silicon-aluminum ratio can be effectively controlled, preventing the imbalance of the silicon-aluminum ratio caused by too fast or too slow dissolution rate of silicon and aluminum, which affects the crystal form and structure of the molecular sieve.

[0076] Preventing side reactions from occurring: If the concentration of the NaOH solution is too high, the reaction will be too violent, which may trigger a series of side reactions, generating useless impurity phases and interfering with the normal formation of the molecular sieve; if the concentration is too low, the reaction cannot proceed sufficiently. The 10%-15% concentration effectively avoids these problems and ensures the high efficiency and selectivity of the reaction.

[0077] Improving the quality of the product

[0078] Promoting crystal growth: The appropriate NaOH concentration provides a suitable chemical environment for the nucleation and growth of the molecular sieve crystal, helps the regular growth of the A-type molecular sieve crystal, improves the crystallinity and purity of the product, and makes the generated molecular sieve have a more complete crystal structure and better performance.

[0079] Reducing the generation of miscellaneous crystals: Precise concentration control can reduce the generation of miscellaneous crystals, avoid the mixing of miscellaneous crystals into the product and reducing the quality of the molecular sieve, and ensure that the finally obtained A-type fly ash-based molecular sieve has high purity and good performance.

[0080] In step 3, the pretreated fly ash and the NaOH solution are mixed at a solid-liquid ratio of 1:4-5.

[0081] The advantages of the above settings are:

[0082] Optimizing reaction kinetics

[0083] Ensure sufficient contact: This solid-liquid ratio can ensure that fly ash particles are fully dispersed in the NaOH solution, maximizing the contact area between the two. Each fly ash particle can come into full contact with the NaOH solution, thereby accelerating the reaction rate, shortening the time required for the alkali dissolution reaction, and improving production efficiency.

[0084] Maintain reaction activity: An appropriate solid-liquid ratio can provide sufficient reaction medium for the reaction, maintain the fluidity of the system, avoid excessive viscosity of the system caused by too high fly ash concentration, which hinders the mass transfer of substances and the progress of the reaction, and ensure smooth mass transfer and heat transfer of substances during the reaction, so that the reaction always maintains a high activity.

[0085] Improve product quality

[0086] Precisely control the silicon-aluminum ratio: A solid-liquid ratio of 1:4 - 5 can precisely control the dissolution amounts of silicon and aluminum during the alkali dissolution process, and then control the silicon-aluminum ratio of the reaction system. This is crucial for the formation of A-type zeolite with a specific crystal structure and properties, and helps to obtain zeolite products with complete crystal form and high crystallinity.

[0087] Reduce impurity generation: A reasonable solid-liquid ratio can avoid side reactions caused by too high or too low reactant concentration, reduce the generation of impurities, improve the purity of the product, and ensure the quality stability of the zeolite product.

[0088] In step 4, by online analyzing the silicon-aluminum concentration of the alkali dissolution reaction solution, dynamically adjusting the concentration and temperature of the NaOH solution, and controlling the silicon-aluminum dissolution rate, ensure that the silicon-aluminum ratio is within a suitable range.

[0089] The advantages of the above settings are as follows:

[0090] Guarantee the stable quality of the product

[0091] Precisely regulate the silicon-aluminum ratio: The silicon-aluminum ratio is a key factor determining the crystal structure and properties of zeolite. Different types of zeolites have strict requirements for the silicon-aluminum ratio, and A-type zeolite requires a specific silicon-aluminum ratio range. By real-time online analyzing the silicon-aluminum concentration and dynamically adjusting the concentration and temperature of the NaOH solution, the silicon-aluminum dissolution rate can be precisely controlled, so that the silicon-aluminum ratio of the reaction system is always maintained within a suitable range, thereby ensuring that A-type zeolite has a stable and compliant crystal structure and greatly improving the quality stability of the product.

[0092] Improve crystallinity and purity: An appropriate silicon-aluminum ratio provides an ideal chemical environment for the growth of zeolite crystals, helps to form a highly ordered crystal structure, and significantly improves the crystallinity of the product. At the same time, precisely controlling the reaction conditions can effectively reduce the generation of impurity phases, improve the purity of the zeolite, and meet the strict requirements for zeolite quality in high-end application scenarios.

[0093] Enhance the flexibility and adaptability of the production process

[0094] Coping with raw material fluctuations: Fly ash has a wide range of sources, and its composition may vary due to factors such as power plant fuel and production processes. Through a dynamic adjustment mechanism, it can monitor and respond to changes in raw material composition in real time, and timely adjust the concentration and temperature of the NaOH solution to ensure that qualified Type A zeolite can be successfully produced when using different batches of fly ash, enhancing the adaptability of the production process to raw material changes.

[0095] Optimizing process parameters: During the production process, external conditions such as equipment operating status and environmental temperature may fluctuate. The dynamic adjustment system can quickly adjust reaction parameters based on real-time feedback to ensure that the production process is not interfered by these factors and always operates in the best state.

[0096] In step 5, the aging temperature is 60 - 90 °C, and the aging time is 4 - 12 hours.

[0097] The advantages of the above settings are as follows:

[0098] Promote crystal growth and development

[0099] Appropriate temperature promotes the formation of crystal nuclei: The temperature range of 60 - 90 °C provides suitable energy conditions for the formation of zeolite crystals. Within this temperature range, silicate-aluminate species in the solution can aggregate and arrange more effectively, which is conducive to the formation of crystal nuclei. Higher temperatures can accelerate the movement speed of molecules, making it easier for silicate-aluminate ions to collide and combine with each other, thus increasing the formation rate of crystal nuclei.

[0100] Sufficient time ensures crystal growth: The aging time of 4 - 12 hours provides sufficient time for crystal growth. During the aging process, crystal nuclei continuously absorb silicate-aluminate ions in the surrounding solution and gradually grow into zeolite crystals with a certain size and structure. A sufficiently long time can make the crystals grow more completely and regularly, improving the crystallinity and purity of the crystals.

[0101] Improve product performance and quality

[0102] Optimize the crystal structure: Appropriate aging temperature and time contribute to the formation of the unique crystal structure of Type A zeolite. At a temperature of 60 - 90 °C and after aging for 4 - 12 hours, silicate-aluminate ions can be orderly assembled according to a specific lattice arrangement to form Type A zeolite with a uniform pore size and good pore structure. This optimized crystal structure enables the zeolite to have a higher specific surface area and better adsorption performance, ion exchange performance, etc., thereby improving the quality and performance of the product.

[0103] Reducing impurities and defects: Appropriate aging conditions can make the impurities in the reaction system more easily excluded from the crystal structure, reduce the inclusion of impurities in the crystal, and lower the defect density of the crystal. This helps to improve the purity and stability of the molecular sieve, enabling it to exhibit better performance and service life in practical applications.

[0104] In step 6, the crystallization temperature is 80 - 120 °C, and the crystallization time is 4 - 12 hours.

[0105] The advantages of the above settings are as follows:

[0106] Providing an ideal thermodynamic environment: The crystallization temperature of 80 - 120 °C provides suitable thermodynamic conditions for the nucleation and growth of molecular sieve crystals. Within this temperature range, the silicate-aluminate species in the reaction system have sufficient activity to overcome the energy barrier of crystal growth, prompting them to arrange according to the crystal structure rules of type A molecular sieve. This effectively avoids slow crystal growth and incomplete crystal forms due to too low temperature, or side reactions and the formation of miscellaneous crystals due to too high temperature, ensuring that the final product has high purity and a complete crystal structure.

[0107] Sufficient time to perfect the crystal structure: The crystallization time of 4 - 12 hours allows the crystals sufficient time to grow and develop. As time goes by, the crystal nuclei continuously absorb the surrounding silicate-aluminate ions and gradually grow into molecular sieve crystals with uniform size and high crystallinity. This not only ensures that the product has good adsorption performance and ion exchange performance, but also improves the stability and service life of the molecular sieve.

[0108] In step 7, by online analyzing the silicon-aluminum concentration and pH value of the crystallization reaction solution, the concentration and temperature of the NaOH solution are dynamically adjusted to control the crystallization process.

[0109] The advantages of the above settings are as follows:

[0110] Ensuring the stability and uniformity of product quality

[0111] Precisely controlling the silicon-aluminum ratio: The silicon-aluminum ratio is a key factor affecting the crystal structure and performance of type A molecular sieve. Different silicon-aluminum ratios will result in molecular sieves with different pore sizes, adsorption properties, ion exchange capabilities, etc. By online analyzing the silicon-aluminum concentration of the crystallization reaction solution, the changes in the silicon and aluminum content in the reaction system can be grasped in real time, and the concentration and temperature of the NaOH solution can be dynamically adjusted, thereby precisely controlling the dissolution and crystallization rates of silicon and aluminum, ensuring that the reaction always proceeds under suitable silicon-aluminum ratio conditions, and further ensuring that each batch of type A molecular sieve produced has a stable crystal structure and consistent performance.

[0112] Maintain a suitable pH environment: The pH value has an important influence on the crystallization process of molecular sieves. Different pH values will affect the existence form and reaction activity of aluminosilicates, thereby affecting the nucleation and growth rates of crystals. By monitoring the pH value in real time and dynamically adjusting the concentration of the NaOH solution, the pH value of the reaction system can be maintained within the range conducive to the crystallization of type A molecular sieves. A suitable pH environment helps to form a regular and complete crystal structure, improve the crystallinity and purity of the product, reduce the generation of impurity phases, and ensure the uniformity of product quality.

[0113] Improve production efficiency and flexibility

[0114] Adjust reaction conditions in a timely manner: The crystallization process is a complex dynamic process affected by various factors, and the reaction conditions may fluctuate. The on-line analysis system can provide real-time feedback on the changes in the silicon-aluminum concentration and pH value of the crystallization reaction solution. Once it is found that these parameters deviate from the preset optimal range, the concentration and temperature of the NaOH solution can be immediately adjusted dynamically to quickly bring the reaction back to the optimal state. This real-time adjustment avoids slow or failed reactions caused by inappropriate reaction conditions, greatly shortens the crystallization time, and improves production efficiency.

[0115] Adapt to different raw materials and process requirements: The compositions of fly ash raw materials from different sources may vary to some extent, and even for the same batch of raw materials, there may be slight changes in different production batches. In addition, different production processes and product requirements also require different crystallization conditions. Through the dynamic adjustment mechanism, the reaction conditions in the crystallization process can be flexibly adjusted according to the actual situation of the raw materials and specific production requirements to ensure that type A molecular sieves meeting quality standards can be produced under various circumstances, improving the flexibility and adaptability of the production process.

[0116] In step 7, by on-line analyzing the silicon-aluminum concentration and pH value of the crystallization reaction solution, when the pH value is lower than 12, add NaOH solution to maintain the pH value at 12 - 13; when the silicon-aluminum ratio is lower than 1.6, raise the reaction temperature to 110 - 120 °C to control the crystallization process.

[0117] The advantages of the above settings are as follows:

[0118] Precise control of pH value: Maintaining the pH value at 12 - 13 is because this range is a suitable alkaline environment for the crystallization of type A molecular sieves. When the pH value is lower than 12, adding NaOH solution can ensure the stability of the alkalinity of the reaction system, which is conducive to the existence of aluminosilicate species in a suitable form and their participation in the crystallization reaction. Under this alkaline condition, the polymerization and depolymerization reactions of aluminosilicates can proceed orderly, promoting the nucleation and growth of molecular sieve crystals, ensuring the integrity and regularity of the crystal structure, and thus improving the quality and performance of the molecular sieve product.

[0119] Synergistic regulation of silica-alumina ratio and temperature: When the silica-alumina ratio is less than 1.6, raising the reaction temperature to 110 - 120 °C is an ingenious synergistic regulation mechanism. The increase in temperature can accelerate the dissolution and reaction rate of aluminosilicates, making the silicon and aluminum species in the system more active, which helps to promote the balance adjustment of the silica-alumina ratio. Within this temperature range, the reaction activity of aluminosilicates is enhanced, enabling more effective ion exchange and crystal structure construction, making the silica-alumina ratio develop towards a suitable range, further optimizing the crystal structure of the molecular sieve, and enhancing its adsorption, catalytic and other properties.

[0120] In step 9, the separation is carried out by centrifugal separation or filtration separation, the washing is carried out with deionized water, and the drying temperature is 100 - 120 °C.

[0121] The advantages of the above settings are:

[0122] Advantages of the separation method

[0123] Centrifugal separation: Centrifugal separation uses the centrifugal force generated by the high-speed rotation of a centrifuge to quickly sediment solid particles in a suspension, thus achieving solid-liquid separation. This separation method has high efficiency and can effectively separate solids and liquids in a short time. It is suitable for treating suspensions of fine particles. For the separation of type A molecular sieves, it can ensure a high recovery rate and reduce the loss of products during the separation process.

[0124] Filtration separation: Filtration separation is to carry out solid-liquid separation of a suspension through a filtration medium, allowing the liquid to pass through the filtration medium while the solid particles are intercepted. This method is relatively simple to operate, has a low equipment cost, and different pore-sized filtration media can be selected according to needs to adapt to type A molecular sieve particles of different particle sizes and ensure the separation effect. At the same time, the filtration separation process has little impact on the physical properties of the product, which helps to maintain the crystal structure and performance of the molecular sieve.

[0125] Advantages of the washing method

[0126] Washing with deionized water can effectively remove the impurity ions adsorbed on the surface of the molecular sieve and the residual reaction reagents. Deionized water contains almost no various ions and will not introduce new impurities, which can ensure the washing effect and improve the purity of the product. Moreover, deionized water is relatively widely available and has a low cost, making it an economical and practical washing medium.

[0127] Advantages of the drying method

[0128] The drying temperature is set at 100 - 120 °C. Within this temperature range, not only can the moisture on the surface and inside of the molecular sieve be rapidly evaporated to achieve efficient drying, but also the destruction or change of the crystal structure of the molecular sieve caused by too high temperature can be avoided. This temperature range is conducive to removing the moisture in the pores of the molecular sieve while maintaining the stability and integrity of its crystal structure, thereby ensuring that the adsorption performance and other physical and chemical properties of the molecular sieve are not affected. In addition, this temperature range is relatively easy to control and easy to implement in industrial production, which can ensure the stability and repeatability of the drying process and is conducive to large-scale production.

[0129] Example 2

[0130] A method for preparing A-type fly ash-based molecular sieve by dynamic self-regulating hydrothermal method, comprising the following steps:

[0131] Step 1. Pretreat the fly ash raw material:

[0132] Step 101. Weigh the raw fly ash powder and dry it at 100 °C until constant weight;

[0133] Step 102. Mix the dried fly ash with a hydrochloric acid solution with a mass percentage concentration of 20% at a solid-liquid ratio of 1:20, and magnetically stir at 80 °C for 12 hours;

[0134] Step 103. Centrifuge at a centrifugal speed of 4000 rpm for 40 minutes, wash the filter cake with deionized water to remove the residual hydrochloric acid until the pH of the washing liquid is 7, and dry the filter cake for standby.

[0135] Step 2. Prepare the alkali solution:

[0136] Weigh analytical pure NaOH and prepare a NaOH solution with a mass percentage concentration of 10% as the alkali solution.

[0137] Step 3. Mix the pretreated fly ash with the alkali solution and carry out an alkali dissolution reaction:

[0138] Mix the pretreated fly ash obtained in Step 1 with the NaOH solution prepared in Step 2 at a solid-liquid ratio of 1:5, and stir at 90 °C for 4 hours to carry out the alkali dissolution reaction.

[0139] Step 4. Carry out on-line analysis of the alkali dissolution reaction solution and dynamically and adaptively adjust the silicon-aluminum dissolution rate of the alkali dissolution process:

[0140] By on-line analyzing the silicon-aluminum concentration of the alkali dissolution reaction solution, when the silicon-aluminum ratio is lower than 1.8, increase the concentration of the NaOH solution to 15%; when the silicon-aluminum ratio is higher than 2.2, lower the reaction temperature to 80 °C, control the silicon-aluminum dissolution rate, and ensure that the silicon-aluminum ratio is within the range of 1.8 - 2.2.

[0141] Step 5. Aging reaction:

[0142] Age the alkali dissolution reaction solution obtained in Step 4 at 70 °C for 8 hours.

[0143] Step 6, crystallization reaction:

[0144] Crystallize the aging solution obtained in Step 5 at 100 °C for 8 hours.

[0145] Step 7, conduct on-line analysis of the crystallization reaction solution and dynamically and adaptively adjust the crystallization process:

[0146] By on-line analyzing the silicon-aluminum concentration and pH value of the crystallization reaction solution, when the pH value is lower than 12, add NaOH solution to maintain the pH value at 12 - 13; when the silicon-aluminum ratio is lower than 1.6, raise the reaction temperature to 110 °C to control the crystallization process.

[0147] Step 8, determine whether the crystallization reaction is completed. If not, return to Step 6. If completed, execute Step 9.

[0148] Step 9, separate, wash, and dry to obtain the A-type fly ash-based molecular sieve product:

[0149] Separate the crystal product by centrifugation, wash it with deionized water until the pH of the filtrate is 7, and dry it at 110 °C for 12 hours to obtain the A-type fly ash-based molecular sieve product.

[0150] Example 3

[0151] A method for preparing A-type fly ash-based molecular sieve by dynamic self-adjusting hydrothermal method, comprising the following steps:

[0152] Step 1, pre-treat the fly ash raw material:

[0153] Step 101, weigh the fly ash raw powder and dry it at 100 °C until constant weight;

[0154] Step 102, mix the dried fly ash with a hydrochloric acid solution with a mass percentage concentration of 25% at a solid-liquid ratio of 1:15, and magnetically stir at 90 °C for 10 hours;

[0155] Step 103, centrifuge at a centrifugal speed of 5000 rpm for 30 minutes, wash the filter cake with deionized water to remove residual hydrochloric acid until the pH of the washing solution is 7, and dry the filter cake for standby.

[0156] Step 2, prepare the alkali solution:

[0157] Weigh analytical pure NaOH and prepare a NaOH solution with a mass percentage concentration of 12% as the alkali solution.

[0158] Step 3, mix the pre-treated fly ash with the alkali solution for alkali dissolution reaction:

[0159] Mix the pretreated fly ash obtained in Step 1 with the NaOH solution prepared in Step 2 at a solid-liquid ratio of 1:4, and carry out an alkali dissolution reaction by stirring at 85°C for 5 hours.

[0160] Step 4: Conduct an on-line analysis of the alkali dissolution reaction solution, and dynamically and adaptively adjust the silicon-aluminum dissolution rate during the alkali dissolution process:

[0161] By on-line analyzing the silicon-aluminum concentration of the alkali dissolution reaction solution, when the silicon-aluminum ratio is lower than 1.7, increase the concentration of the NaOH solution to 16%; when the silicon-aluminum ratio is higher than 2.3, lower the reaction temperature to 75°C, control the silicon-aluminum dissolution rate, and ensure that the silicon-aluminum ratio is within the range of 1.7 - 2.3.

[0162] Step 5: Aging reaction:

[0163] Age the alkali dissolution reaction solution obtained in Step 4 at 80°C for 10 hours.

[0164] Step 6: Crystallization reaction:

[0165] Crystallize the aging solution obtained in Step 5 at 95°C for 10 hours.

[0166] Step 7: Conduct an on-line analysis of the crystallization reaction solution, and dynamically and adaptively adjust the crystallization process:

[0167] By on-line analyzing the silicon-aluminum concentration and pH value of the crystallization reaction solution, when the pH value is higher than 13.5, add hydrochloric acid solution to maintain the pH value at 12.5 - 13; when the silicon-aluminum ratio is higher than 1.8, lower the reaction temperature to 90°C to control the crystallization process.

[0168] Step 8: Judge whether the crystallization reaction is completed. If not, return to Step 6; if completed, execute Step 9.

[0169] Step 9: Separate, wash, and dry to obtain the A-type fly ash-based molecular sieve product:

[0170] Separate the crystal product by filtration, wash it with deionized water until the pH of the filtrate is 7, and dry it at 105°C for 10 hours to obtain the A-type fly ash-based molecular sieve product.

[0171] Specific experiments

[0172] Experimental materials and equipment

[0173] Materials: Fly ash with various silicon-aluminum ratios, sodium hydroxide, deionized water, etc.

[0174] Equipment: A dynamic hydrothermal reactor equipped with an automatic sampling device, an elemental analyzer, and an in-situ Raman spectrometer, and equipped with a PLC or DCS control system; detection equipment such as an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a nitrogen adsorption-desorption analyzer, and a thermogravimetric analyzer (TGA).

[0175] Experimental procedures

[0176] Sample preparation: Select fly ashes with different silica-alumina ratios, numbered A, B, C, etc. respectively.

[0177] Set up comparative experiments:

[0178] Experimental group: Adopt the dynamic self-adjusting hydrothermal method. Taking fly ash A as an example, add it to the dynamic hydrothermal reactor, add an appropriate amount of sodium hydroxide solution and deionized water, set the initial alkali dissolution temperature and stirring speed, automatically sample the material in the equilibrium tube according to the preset sampling period, perform elemental analysis on the liquid phase after automatic filtration, and use the PLC or DCS system to adopt an autonomous optimization method to adjust the alkali dissolution temperature and stirring speed in real time according to the silica-alumina ratio of the liquid phase. When the ratio of the sum of the silicon-aluminum ion concentrations to the sodium ion concentration reaches the critical value and the silica-alumina ratio meets the set range, end the alkali dissolution and start the aging. After aging, carry out crystallization, set the initial crystallization temperature and stirring speed of the reactor, also automatically sample the material according to the preset sampling period, perform elemental analysis on the liquid phase, perform in-situ Raman spectroscopy analysis on the solid phase, and adjust the crystallization temperature, crystallization time and stirring speed in real time according to the analysis results until the product requirements are met or after the maximum crystallization time, stop crystallization and cool down. Treat fly ashes B, C, etc. in the same way.

[0179] Control group: Adopt the traditional hydrothermal method. Respectively take the same fly ashes A, B, C, etc. as the experimental group, add them to a common hydrothermal reactor, add the same amount of sodium hydroxide solution and deionized water, and carry out reactions according to fixed parameters such as alkali dissolution temperature, stirring speed, crystallization temperature, crystallization time, etc., without dynamic adjustment.

[0180] Product detection:

[0181] Perform XRD analysis on the molecular sieve products obtained from the two groups of experiments to compare the integrity and purity of the crystal structures.

[0182] Use SEM to observe the crystal morphology and measure the crystal particle size distribution.

[0183] Determine the specific surface area and pore volume of the molecular sieve through a nitrogen adsorption-desorption analyzer.

[0184] Use TGA to determine the water content and thermal stability of the product.

[0185] Record the energy consumption during each experimental process, including the power consumption during heating, stirring, etc.

[0186] Verification of Expected Results and Advantages

[0187] Improvement in Product Quality:

[0188] The crystal structure of the products in the experimental group is more complete and has higher purity; the crystal structure of the products in the control group is relatively poor.

[0189] In the SEM images, the crystal morphology of the experimental group is more regular and the particle size distribution is more uniform; the crystals in the control group may have different sizes and irregular shapes.

[0190] The results of nitrogen adsorption - desorption tests show that the specific surface area and pore volume of the experimental group are larger, indicating that the dynamic self - regulating hydrothermal method can effectively optimize the pore structure of the molecular sieve and improve its adsorption performance.

[0191] Enhanced Process Stability:

[0192] For fly ashes with different silica - alumina ratios, the experimental group can obtain products with stable quality through dynamic adjustment, proving that this method has strong adaptability to raw materials and is not affected by the differences in the chemical composition and mineral activity of fly ash itself; while for the control group, the product quality may fluctuate greatly when using different fly ashes.

[0193] Reduction in Energy Consumption:

[0194] Since the experimental group can adjust parameters such as temperature and stirring speed in real time according to the reaction conditions, avoiding unnecessary high temperatures and long - time stirring, the energy consumption records show that the power consumption of the experimental group is significantly lower than that of the control group, indicating that the dynamic self - regulating hydrothermal method has the advantage of low energy consumption.

[0195] The examples given in the present invention are illustrative rather than restrictive of the implementation manners. For those of ordinary skill in the art, based on the above description, other different forms of changes or modifications can be made. It is not necessary and impossible to enumerate all implementation manners here, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method, characterized in that: The following steps are involved: Step 1, pre-treating fly ash raw materials; Step 2, preparing an alkaline solution; Step 3, mixing the pretreated fly ash with an alkaline solution to perform an alkaline dissolution reaction; Step 4, analyzing the alkali dissolution reaction liquid online, and dynamically and adaptively adjusting the silicon and aluminum dissolution rate in the alkali dissolution process; Step 5, aging reaction; Step 6, crystallization reaction; Step 7, analyzing the crystallization reaction solution online, and dynamically and adaptively adjusting the crystallization process; Step 8, determine whether the crystallization reaction is completed, if not completed, return to step 6, if completed, execute step 9; Step 9: separation, washing and drying to obtain a type A fly ash-based molecular sieve product.

2. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In step 1, the specific method for pretreating the fly ash raw material is: Step 101, weighing fly ash raw powder, and drying it at 100° C. to constant weight; Step 102, mixing the dried fly ash with a hydrochloric acid solution having a mass percentage concentration of 20% at a solid-liquid ratio of 1:20, and magnetically stirring at 80° C. for 12 hours; Step 103, centrifugation is performed at a centrifugal speed of 4000 rpm for 40 minutes, the filter cake is washed with deionized water to remove residual hydrochloric acid until the pH of the washing solution is 7, and the filter cake is dried for later use.

3. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In the step 2, the alkaline solution is a NaOH solution with a mass percent concentration of 10%-15%.

4. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In the step 3, the pretreated fly ash is mixed with the NaOH solution at a solid-liquid ratio of 1:4-5.

5. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In step 4, the concentration of silicon and aluminum in the alkaline solution is analyzed online, the concentration and temperature of the NaOH solution are dynamically adjusted, the silicon and aluminum dissolution rate is controlled, and the silicon-aluminum ratio is ensured to be within an appropriate range.

6. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In the step 5, the aging temperature is 60-90° C., and the aging time is 4-12 hours.

7. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In step 6, the crystallization temperature is 80-120° C., and the crystallization time is 4-12 hours.

8. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In step 7, the concentration and temperature of the NaOH solution are dynamically adjusted by online analyzing the silicon-aluminum concentration and pH value of the crystallization reaction solution to control the crystallization process.

9. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 8, characterized in that: In step 7, the silicon-aluminum concentration and pH value of the crystallization reaction solution are analyzed online. When the pH value is lower than 12, NaOH solution is added to maintain the pH value at 12-13; when the silicon-aluminum ratio is lower than 1.6, the reaction temperature is increased to 110-120°C to control the crystallization process.

10. The method for preparing type A fly ash-based molecular sieve by a dynamic self-regulating hydrothermal method according to claim 1, characterized in that: In step 9, separation is performed by centrifugation or filtration, washing is performed by deionized water, and the drying temperature is 100-120°C.

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