A method for preparing a sodalite-type zeolite molecular sieve from fly ash and a product thereof

Abstract

The application discloses a method for preparing sodalite type zeolite molecular sieve by using fly ash and a product thereof, and the method comprises the following steps: mixing dry and ground fly ash and sodium hydroxide according to a mass ratio of 1:0.8-1.0, then transferring the mixture into a reaction kettle with tetrafluoroethylene lining, placing the reaction kettle in an oven, and performing hot-pressing reaction at 160-180 DEG C and 1.2-1.5 MPa for 9-18 h, after the reaction is completed, washing the product with distilled water until the washing liquid is neutral, filtering and drying the filter residue, and then the sodalite type zeolite molecular sieve is obtained. The application provides a method for efficiently and low-energy-consumption grinding-hot-pressing-washing synthesis of sodalite type zeolite molecular sieve, and the obtained sodalite has high purity, good crystallinity and uniform morphology. The application provides a new way for resource utilization of fly ash and synthesis of zeolite, and has remarkable economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to a method for preparing zeolite molecular sieves, and more particularly to a method for preparing sodalite-type zeolite molecular sieves by utilizing the silica-alumina components in fly ash in a highly efficient and low-energy-consumption manner. This method belongs to the fields of solid waste resource utilization and zeolite molecular sieve synthesis. Background Technology

[0002] Fly ash is a solid waste residue left after coal combustion. As of 2020, my country's annual coal consumption was approximately 4.98 billion tons, generating over 600 million tons of fly ash annually, and this figure continues to rise. A large portion of this fly ash is piled up in abandoned sites, causing irreparable damage to soil and water resources due to accumulation and rainwater seepage.

[0003] Zeolite is a three-dimensional aluminosilicate crystalline mineral composed of alkaline earth or alkali metals, with silicon, aluminum, and oxygen as its basic framework elements. The formation of the zeolite crystal structure mainly involves four processes: 1) primary structural unit—TO4 tetrahedron (T = Si, Al); 2) secondary structural unit—multi-ring structure, where TO4 tetrahedrons are connected by shared oxygen atoms; 3) constituent building unit—cage structure, where multi-rings form the zeolite framework in different ways; and 4) characteristic chain and layered structural units. In the zeolite framework, some aluminum atoms replace silicon atoms, making the entire structural unit electronegative. Due to its porous structure and electronegativity, zeolite possesses both physical and chemical adsorption capabilities.

[0004] Sodalite is an important inorganic functional material belonging to the cubic crystal system. Its structure consists of β-cages or SOD cages linked by single six- or single four-membered rings, with sodium ions acting as a stabilizing framework. This structure gives sodalite-type zeolites a large specific surface area and pore volume, which is beneficial for adsorbing and storing molecules. It also exhibits good catalytic properties, making it suitable as a catalyst or catalyst support. Furthermore, it can be exchanged with other ions (such as hydrogen ions and ammonium ions), thereby altering its chemical properties and adsorption performance. This ion exchange capability makes sodalite-type zeolites widely used in water treatment, ion exchange resins, and other fields. Its pore structure, adsorption performance, catalytic performance, and ion exchange performance make it valuable for applications in various fields.

[0005] The traditional method for synthesizing sodalite is the hydrothermal method. The hydrothermal method is complex, requires high-temperature activation of fly ash, resulting in high energy consumption, and generates a large amount of alkaline waste liquid after the reaction, causing problems for the environment and subsequent treatment.

[0006] Chinese patent CN201811101703.8 describes a method for preparing hydroxysatite using a hydrothermal method with sub-molten salt in fly ash, which employs a traditional hydrothermal method. The difficulty in using this method to prepare hydroxysatite from the silica-alumina components of fly ash lies in the initial need to dissolve inert substances such as mullite in the fly ash. Furthermore, these substances are difficult to dissolve in solvents under high-concentration alkaline solutions or high-pressure conditions, requiring high-pressure alkaline dissolution. In this patent, a large amount of sodium hydroxide solution is added during the first round of dissolving the inert substances. The mass fraction of sodium hydroxide is 30%–60%, and the required mass of sodium hydroxide solution is 5–20 times that of fly ash, while the mass of sodium hydroxide is 1.5–12 times that of fly ash. The reaction temperature is not lower than 220℃. During the reaction, the aqueous solution in the reactor transforms into a gaseous state, with a volume hundreds of times larger than the aqueous solution. When a large amount of water vapor accumulates, the gas pressure inside the reactor becomes excessively high, placing high demands on the quality of the equipment and posing a significant safety hazard. Chinese patent CN201611091610.2, concerning a method for preparing sodalite and ZSM-5 molecular sieves from fly ash acid extraction residue and a method for utilizing fly ash, also employs the traditional hydrothermal method for preparing sodalite. In this patent, the raw materials are activated by roasting at 830℃~890℃ for 60min~120min, converting the inert components in the fly ash into soluble salts. Then, the activated soluble salts are dissolved in an aqueous solution at a reaction temperature of 90℃~120℃ for 10min~60min. During crystallization, the crystallization time reaches a maximum of 48 hours, and the crystallization temperature is 90℃~120℃. This still presents the problem of the aqueous solution turning into water vapor, leading to excessive pressure in the reaction vessel. While this method facilitates the dissolution of silica and alumina components from fly ash slag, synthesizes sodalite, and improves the utilization rate of fly ash, it also presents several drawbacks, including high activation temperature, high energy consumption, long crystallization time, complex reaction process, cumbersome operation, high requirements for reaction equipment, and high risks during crystallization. Therefore, developing a simpler method to replace the current complex hydrothermal synthesis method for the efficient synthesis of sodalite, and opening up a new pathway or method for the resource utilization of fly ash, is imperative.

[0007] A search revealed no reports on the method of synthesizing sodalite-type zeolite molecular sieves at a lower temperature using fly ash, a byproduct of the coal industry, as raw material through alkali activation, in order to achieve the tiered utilization of industrial solid waste. This method fully utilizes the silicon and aluminum components in fly ash and employs processes such as grinding, hot pressing, and washing to synthesize sodalite-type zeolite molecular sieves efficiently and with low energy consumption. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing sodalite-type zeolite molecular sieves using the silica-alumina components in fly ash in a highly efficient and low-energy-consumption manner.

[0009] The method for preparing sodalite-type zeolite molecular sieves using fly ash according to the present invention comprises the following steps:

[0010] (1) Raw material grinding, sieving, and mixing process:

[0011] Place the fly ash in a drying oven and dry it at 140±10℃ for 6±2h. Grind it and sieve it through a 100-mesh sieve for later use. Grind the sodium hydroxide solid and sieve it through a 100-mesh sieve for later use. Then, mix the sieved fly ash and sodium hydroxide powder evenly at a mass ratio of fly ash to sodium hydroxide of 1:0.8-1.0.

[0012] (2) Hot pressing treatment:

[0013] The mixture in step (1) is transferred to a reaction vessel with a polytetrafluoroethylene liner and placed in an oven at 160-180℃ and 1.2-1.5MPa for hot pressing reaction for 9-18 hours. After the reaction is completed, it is cooled to room temperature and the reaction product is taken out.

[0014] (3) Washing treatment:

[0015] The product obtained in step 2) is thoroughly washed with distilled water until the washing liquid is neutral. The product is then filtered and the filter residue is placed in a drying oven and dried at 140±10℃ for 8±2h to obtain sodalite-type zeolite molecular sieve.

[0016] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the preferred drying temperature of the fly ash in step (1) is 140℃.

[0017] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the preferred drying time for fly ash in step (1) is 6 hours.

[0018] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the preferred mass ratio of fly ash to sodium hydroxide in step (1) is 1:0.9.

[0019] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the amount of the mixture added to the reactor in step (2) is preferably 1 / 2 of the reactor lining volume.

[0020] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the hot pressing reaction temperature in the oven in step (2) is preferably 170℃.

[0021] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the hot pressing reaction pressure in the oven in step (2) is preferably 1.4 MPa.

[0022] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the hot pressing reaction time in the oven in step (2) is preferably 15 hours.

[0023] In the above method for preparing sodalite-type zeolite molecular sieves using fly ash: the filter residue in step (3) is preferably placed in a drying oven and dried at 140°C for 8 hours.

[0024] The product obtained by the above method for preparing sodalite-type zeolite molecular sieves using fly ash.

[0025] This invention provides a highly efficient and low-energy-consumption method for synthesizing sodalite-type zeolite molecular sieves through grinding, hot pressing, and washing. This offers a new approach to solving the problems of difficult fly ash treatment and low economic efficiency, and also provides a new method for the preparation of sodalite. Compared to a method for preparing hydroxyl sodalite using a sub-molten salt alkaline hydrothermal method with fly ash, the significant difference lies in the fact that this invention employs a solid-phase reaction. The fly ash's activity is enhanced by alkali activation, and sodalite is directly synthesized through hot pressing under relatively low temperature and pressure conditions. The amount of alkali used is 0.8-1.0 times the mass of the fly ash. The small amount of alkali results in the production of gaseous products from trace amounts of organic matter in the reactants, and the small amount of air in the reactor experiences increased molecular motion and pressure under the influence of temperature. However, the maximum pressure increase is less than 5 times, far below the reactor's tolerance limit, resulting in lower equipment requirements and higher safety. Compared with methods for preparing sodalite and ZSM-5 molecular sieves from fly ash acid extraction residue and methods for utilizing fly ash, the significant difference of this invention lies in its simultaneous activation and synthesis method. Using a solid-phase reaction, the fly ash is activated by alkali, increasing its activity and directly promoting sodalite nucleation and crystal growth. This method is simple to operate, has a low reaction temperature, is easy to control, and is highly safe. Experimental tests confirm that the zeolite product synthesized by the method provided in this invention has few impurity peaks in its XRD pattern; the XRD pattern shows high crystallinity; the SEM shows a uniform crystal structure; and the infrared spectrum of the obtained zeolite exhibits the characteristic absorption peaks of sodalite-type zeolite. This invention demonstrates that it achieves efficient synthesis of sodalite through a simpler method than the previous complex hydrothermal synthesis method, with simple operation and easy control. It provides a new approach and method for the resource utilization of fly ash and the synthesis of zeolite, with significant economic and environmental benefits. Attached Figure Description

[0026] Figure 1 XRD pattern of fly ash raw material;

[0027] Figure 2 SEM image of fly ash raw material;

[0028] Figure 3 This is the XRD pattern of sodium silicate in Example 1 of the present invention;

[0029] Figure 4This is a SEM image of sodium silicate from Example 1 of the present invention;

[0030] Figure 5 This is the FTIR spectrum of sodium silicate in Example 1 of the present invention;

[0031] Figure 6 This is the XRD pattern of sodium silicate in Example 2 of the present invention;

[0032] Figure 7 This is a SEM image of sodalite in Example 2 of the present invention;

[0033] Figure 8 This is the FTIR spectrum of sodium silicate in Example 2 of the present invention;

[0034] Figure 9 This is the XRD pattern of sodium silicate in Example 3 of the present invention;

[0035] Figure 10 This is a SEM image of sodium silicate from Example 3 of the present invention;

[0036] Figure 11 This is the FTIR spectrum of sodium carbonate in Example 3 of the present invention. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific accompanying drawings and embodiments. The examples described below are merely preferred embodiments of the present invention. It should be noted that the following description is only for explaining the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

[0038] In the following examples, all reagents used were conventional materials and, unless otherwise specified, were obtained commercially. Fly ash was obtained from a power plant and is industrial waste.

[0039] Example 1: Preparation of sodalite-type zeolite molecular sieves

[0040] (1) Raw material grinding, sieving, and mixing process:

[0041] The fly ash from the power plant was placed in a drying oven and dried at 140℃ for 6 hours. After grinding, it was sieved through a 100-mesh sieve and set aside. The sodium hydroxide solid was ground and sieved through a 100-mesh sieve and set aside. Then, the sieved fly ash and sodium hydroxide powder were mixed evenly at a ratio of 5.0g fly ash to 4.0g sodium hydroxide powder.

[0042] (2) Hot pressing treatment:

[0043] The mixture in step (1) was transferred to a reaction vessel with a polytetrafluoroethylene liner. The amount of mixture added to the reaction vessel was 1 / 2 of the volume of the reaction vessel liner. The mixture was placed in an oven and subjected to hot pressing reaction at 180°C and 1.5MPa for 9 hours. After the reaction was completed, the mixture was cooled to room temperature and the reaction product was removed.

[0044] (3) Washing treatment:

[0045] The product obtained in step 2) is thoroughly washed with distilled water until the washing liquid is neutral. The product is then filtered and the filter residue is placed in a drying oven and dried at 140°C for 8 hours to obtain sodalite-type zeolite molecular sieve.

[0046] The product obtained by the above method for preparing sodalite-type zeolite molecular sieves using fly ash, and the test results of the sodalite-type zeolite molecular sieves are shown in [the table below]. Figures 3-5 .

[0047] Example 2: Preparation of sodalite-type zeolite molecular sieves

[0048] (1) Raw material grinding, sieving, and mixing process:

[0049] The fly ash from the power plant was placed in a drying oven and dried at 140℃ for 6 hours. It was then ground and sieved through a 100-mesh sieve for later use (this step provides sufficiently fine fly ash raw material for the subsequent process and ensures uniform fly ash particle size, allowing for a more complete reaction in the following reaction). Sodium hydroxide solid was ground and sieved through a 100-mesh sieve for later use (this step serves the same purpose as grinding the fly ash). Then, the sieved fly ash and sodium hydroxide powder were mixed evenly at a ratio of 5.0g fly ash to 5.0g sodium hydroxide powder (this ensures sufficient contact between the fly ash and sodium hydroxide, providing favorable reaction conditions for the subsequent reaction (maximizing the contact area for the solid-phase reaction)). The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results of the fly ash powder are shown below. Figure 1 , Figure 2 As shown.

[0050] (2) Hot pressing treatment:

[0051] The mixture in step (1) was transferred to a reaction vessel with a polytetrafluoroethylene liner. The amount of mixture added to the reaction vessel was 1 / 2 of the volume of the reaction vessel liner. The mixture was placed in an oven and subjected to hot pressing reaction at 170°C and 1.4 MPa for 15 hours. After the reaction was completed, the mixture was cooled to room temperature and the reaction product was removed.

[0052] (3) Washing treatment:

[0053] The product obtained in step 2) is thoroughly washed with distilled water until the washing liquid is neutral. The product is then filtered and the filter residue is placed in a drying oven and dried at 140°C for 8 hours to obtain sodalite-type zeolite molecular sieve.

[0054] The product obtained by the above method for preparing sodalite-type zeolite molecular sieves using fly ash, and the test results of the sodalite-type zeolite molecular sieves are shown in [the table below]. Figures 6-8 .

[0055] Example 3: Preparation of sodalite-type zeolite molecular sieves

[0056] (1) Raw material grinding, sieving, and mixing process:

[0057] The fly ash from the power plant was placed in a drying oven and dried at 140℃ for 6 hours. After grinding, it was sieved through a 100-mesh sieve and set aside. The sodium hydroxide solid was ground and sieved through a 100-mesh sieve and set aside. Then, the sieved fly ash and sodium hydroxide powder were mixed evenly at a ratio of 5.0g fly ash to 4.5g sodium hydroxide powder.

[0058] (2) Hot pressing treatment:

[0059] The mixture in step (1) was transferred to a reaction vessel with a polytetrafluoroethylene liner. The amount of mixture added to the reaction vessel was 1 / 2 of the volume of the reaction vessel liner. The mixture was placed in an oven and subjected to hot pressing reaction at 160°C and 1.3MPa for 18 hours. After the reaction was completed, the mixture was cooled to room temperature and the reaction product was removed.

[0060] (3) Washing treatment:

[0061] The product obtained in step 2) is thoroughly washed with distilled water until the washing liquid is neutral. The product is then filtered and the filter residue is placed in a drying oven and dried at 140°C for 8 hours to obtain sodalite-type zeolite molecular sieve.

[0062] The product obtained by the above method for preparing sodalite-type zeolite molecular sieves using fly ash, and the test results of the sodalite-type zeolite molecular sieves are shown in [the table below]. Figures 9-11 .

[0063] This invention employs a solid-state reaction, enhancing the activity of fly ash through alkali activation. Sodalite is then directly synthesized via hot pressing under relatively low temperature and pressure conditions. Simultaneously, this invention utilizes a simultaneous activation and synthesis method. By enhancing the activity of fly ash through alkali activation via a solid-state reaction, the nucleation and subsequent crystal growth of sodalite are directly promoted. This method is simple to operate, involves low reaction temperatures, is easy to control, and offers high safety. It achieves a simpler and more efficient synthesis of sodalite than the previously complex hydrothermal synthesis method, providing a new pathway and approach for the resource utilization of fly ash and the synthesis of zeolites.

[0064] The test results show that the XRD pattern of the zeolite product synthesized by the above method has few impurity peaks; the XRD pattern shows that the crystallinity is high; the SEM shows that the crystal morphology and structure are uniform; the infrared spectrum of the synthesized zeolite has the characteristic absorption peaks of sodalite-type zeolite.

[0065] Although the general explanation and specific embodiments of the invention have been described in detail above, certain modifications and improvements can be made based on the invention. Thus, any alterations and improvements made without departing from the spirit of the invention are within the scope of protection of the invention. It should be particularly noted that all similar substitutions and modifications will be apparent to those skilled in the art who believe them to be included in the spirit, scope, and content of the invention.

Claims

1. A method for preparing sodalite-type zeolite molecular sieve using fly ash, comprising the steps of: (1) grinding, sieving and mixing the raw materials: placing the fly ash in a drying oven, drying at 140±10℃ for 6±2h, grinding and sieving through a 100-mesh sieve, and then grinding the sodium hydroxide solid and sieving through a 100-mesh sieve; then uniformly mixing the sieved fly ash and sodium hydroxide powder in a mass ratio of 1:0.8-1.0; (2) heat pressing: transferring the mixture in step (1) to a reaction kettle with a polytetrafluoroethylene lining, placing it in an oven and heat pressing at 160-180℃ and 1.2-1.5 MPa for 9-18h; after the reaction is completed, cooling to room temperature and removing the reaction product; (3) washing: washing the product obtained in step (2) with distilled water until the washing liquid is neutral, filtering and drying the filter residue in a drying oven at 140±10℃ for 8±2h to obtain the sodalite-type zeolite molecular sieve. The fly ash drying temperature in step (1) is 140℃. The fly ash drying time in step (1) is 6h. The mass ratio of fly ash to sodium hydroxide in step (1) is 1:0.

9. The amount of the mixture added to the reaction kettle in step (2) is 1 / 2 of the lining volume of the reaction kettle. The heat pressing temperature in the oven in step (2) is 170℃. The heat pressing pressure in the oven in step (2) is 1.4 MPa.

2. The method for preparing offretite zeolite molecular sieve from fly ash according to claim 1, characterized in that: The heat pressing time in the oven in step (2) is 15h.

3. The method for preparing offretite zeolite molecular sieve from fly ash according to claim 1, characterized in that: The filter residue is dried in a drying oven at 140℃ for 8h in step (3).

4. The method for preparing offretite zeolite molecular sieve from fly ash according to claim 1, characterized in that:

10. The product obtained by the method of claim 1 for preparing sodalite-type zeolite molecular sieve using fly ash.

5. The method for preparing offedite-type zeolite molecular sieves from fly ash according to claim 1, characterized by: ​ 6. The method for preparing offedite-type zeolite molecular sieves from fly ash according to claim 1, characterized in that: ​ 7. The method for preparing offretite zeolite molecular sieve from fly ash according to claim 1, characterized in that: ​ 8. The method for preparing offretite zeolite molecular sieve from fly ash according to claim 1, characterized in that: ​ 9. The method for preparing offedite-type zeolite molecular sieves from fly ash according to claim 1, characterized by: ​ ​

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