A fly ash-based sod-like molecular sieve and a method for preparing the same

Abstract

The application discloses a kind of sod class molecular sieve based on fly ash and preparation method thereof, comprising the following steps: fly ash and alkaline compound are activated by ball milling or grinding at 50-200 DEG C, add lye and floating agent, foam is carried out by gas, after heating, solid-liquid separation treatment is carried out after crystallization treatment and water beating, the solid obtained by drying is sod class molecular sieve.The preparation method of the sod class molecular sieve based on fly ash provided by the application solves the technical problems of the prior art, such as complex raw material composition, high activation energy consumption, low utilization efficiency, low carbon removal efficiency in the synthesis process, insufficient carbon removal, complicated process and large waste liquid production.The preparation method has low raw material activation energy consumption, sufficient carbon removal, simplified steps, reduced cost, and greatly improved the utilization rate of silicon-aluminum oxide components in fly ash and the purity and crystallinity of the prepared sod class molecular sieve.

Description

A SOD-type molecular sieve based on fly ash and its preparation method Technical Field

[0001] This invention relates to the field of molecular sieve preparation technology, specifically to a SOD-type molecular sieve based on fly ash and its preparation method. Background Technology

[0002] Fly ash mainly originates from coal-fired power plants and industrial boiler slag. Its main components include silicon dioxide, alumina, iron oxide, and small amounts of calcium and magnesium oxides, etc. Currently, China's power generation is mainly based on thermal power, generating more than 700 million tons of fly ash annually. The main methods of disposal are landfilling or brick making, resulting in a low comprehensive utilization rate.

[0003] Molecular sieves are aluminosilicates composed of TO4 tetrahedra linked by shared oxygen atoms to form a basic framework. Structurally, they contain numerous uniformly sized channels and neatly arranged pores, with pore sizes comparable to those of typical molecules. Based on their effective pore size, they can sieve various fluid molecules. Molecular sieves possess excellent catalytic, adsorption, and ion exchange properties. SOD-type molecular sieves are a class of molecular sieves composed of SOD cage secondary structural units, including LTA, FAU, SOD, LTN, EMT, FAR, GIU, MAR, TSC, and FRA type molecular sieves.

[0004] Since Holler first synthesized zeolite molecular sieves from fly ash using a hydrothermal method in 1985, researchers have continuously innovated and improved the synthesis methods, obtaining at least 10 types of molecular sieves, including LTA, FAU, and SOD types. However, the silicon and aluminum elements in fly ash are mainly distributed in inert components such as quartz and mullite, making direct extraction difficult. Existing technologies all require mixing fly ash with alkaline compounds and then calcining at high temperatures to activate the inert components in the fly ash. In addition, a large amount of light, insoluble carbon adheres to the surface of fly ash. Existing technologies mostly remove carbon by converting it into carbon dioxide through high-temperature calcination, which is energy-intensive and has low carbon removal efficiency, resulting in problems such as low purity and poor crystallinity of the synthesized molecular sieves, making them difficult to apply in actual production. Summary of the Invention

[0005] To address the above technical problems, the purpose of this invention is to provide a SOD-type molecular sieve based on fly ash and its preparation method.

[0006] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0007] The first aspect of this invention provides a method for preparing SOD-type molecular sieves based on fly ash, comprising the following steps:

[0008] (1) Fly ash and alkaline compounds are activated by ball milling or grinding at 50-200℃, and mixed solution I is obtained after adding alkaline solution;

[0009] (2) Add flotation agent to the mixed solution I in step (1), introduce gas to foam, separate the suspended foam, and obtain mixed solution II;

[0010] (3) Heat the mixed solution II in step (2) to obtain mixed solution III;

[0011] (4) The mixed solution Ⅲ in step (3) is crystallized, and after adding water and pulping, solid-liquid separation is performed. The resulting solid is dried to obtain the SOD molecular sieve.

[0012] This invention employs ball milling or grinding for activation, which reduces the energy consumption for raw material activation. Adding a flotation agent to mixed solution I and introducing gas for foaming blows out light, insoluble impurities in mixed solution I and fixes them in the upper suspended foam, deeply removing residual carbon from the raw materials and further improving the purity of the product. Vigorous stirring during heating of mixed solution II helps to fully dissolve silicon and aluminum elements in fly ash, greatly improving the utilization rate of silicon and aluminum in the raw materials. Adding water and pulping can wash away soluble impurities attached to the product surface and avoids the generation of a large amount of waste liquid from direct rinsing.

[0013] The present invention provides a method for preparing SOD-type molecular sieves based on fly ash, which solves the technical problems of existing technologies such as complex raw material composition, high activation energy consumption, low utilization efficiency, low carbon removal efficiency, insufficient carbon removal, cumbersome process, and large waste liquid production. The preparation method has low raw material activation energy consumption, sufficient carbon removal, simplified steps, reduced cost, and greatly improves the utilization rate of silicon and aluminum oxide components in fly ash and the purity and crystallinity of the prepared SOD-type molecular sieves.

[0014] Further, in step (1), the alkaline compound is selected from one or more of alkali metal oxides, alkali metal hydroxides, alkaline earth metal oxides and alkaline earth metal hydroxides, the alkaline solution is an aqueous solution of alkali metal hydroxide and / or an aqueous solution of alkaline earth metal hydroxide, and the concentration of the alkaline solution is 0.5 to 10 mol / L.

[0015] Further, in step (1), the mass ratio of the fly ash to the alkaline compound is 1:(0.5-50).

[0016] Furthermore, in step (1), the ball milling or grinding time is 3 to 6 hours.

[0017] Preferably, the activation method is ball milling. Using ball milling to crush fly ash can reduce the particle size of the raw material, and the heat released by the collision of steel balls in the ball mill can locally melt the alkali source, increasing the contact area between the fly ash and the molten alkali source. This fully activates the silica and alumina oxides such as quartz and mullite in the fly ash. Furthermore, with an external heating source, the temperature inside the ball mill can be maintained at 50-200°C at a lower power, significantly reducing the energy consumption for raw material activation.

[0018] Further, in step (1), the solid-liquid ratio of the mixed solution I is 1:(10~50)g / mL.

[0019] Further, in step (2), the flotation agent is selected from one or more of oleic acid, kerosene, diesel oil, pine oil and 2-octanol, and the gas is air and / or an inert gas.

[0020] Furthermore, the inert gas is preferably nitrogen, argon, or helium.

[0021] Further, in step (3), the heating temperature is 60-100℃, preferably 70-90℃, and the heating time is 0.5-16h, preferably 2-6h, while the mixture is vigorously stirred during heating.

[0022] Furthermore, step (3) includes a step of replenishing silicon and / or aluminum sources before heating.

[0023] Furthermore, the silicon source is sodium silicate, and the aluminum source is sodium aluminate.

[0024] Furthermore, in step (4), the temperature of the crystallization treatment is 25 to 220°C, the time of the crystallization treatment is 1 to 72 hours, and the crystallization treatment also includes a step of filtering the product after crystallization.

[0025] Furthermore, in step (4), the temperature for adding water and pulping is 30-60°C, and the time for adding water and pulping is 5-60 minutes.

[0026] Furthermore, in step (4), the drying temperature is 80-120°C and the drying time is 4-16 hours.

[0027] Further, in step (4), the skeleton type of the SOD molecular sieve is LTA, FAU, SOD, LTN, EMT, FAR, GIU, MAR, TSC or FRA.

[0028] This method can be used to synthesize molecular sieves including but not limited to LTA, FAU, SOD, and LTN types, and can also be reasonably extended to synthesize other SOD-type molecular sieves such as EMT and FAR.

[0029] The second aspect of the present invention provides a SOD-type molecular sieve prepared by the method described in the first aspect.

[0030] The beneficial effects of this invention are:

[0031] This invention employs ball milling or grinding for activation, which reduces the energy consumption for raw material activation. Adding a flotation agent to mixed solution I and introducing gas for foaming blows out light, insoluble impurities in mixed solution I and fixes them in the upper suspended foam, deeply removing residual carbon from the raw materials and further improving the purity of the product. Vigorous stirring during heating of mixed solution II helps to fully dissolve silicon and aluminum elements in fly ash, greatly improving the utilization rate of silicon and aluminum in the raw materials. Adding water and pulping can wash away soluble impurities attached to the product surface and avoids the generation of a large amount of waste liquid from direct rinsing.

[0032] The present invention provides a method for preparing SOD-type molecular sieves based on fly ash, which has low energy consumption for raw material activation, sufficient carbon removal, simplifies the steps, reduces costs, and greatly improves the utilization rate of silicon and aluminum oxide components in fly ash and the purity and crystallinity of the prepared SOD-type molecular sieves. Attached Figure Description

[0033] Figure 1 is an X-ray diffraction pattern of fly ash in Example 1.

[0034] Figure 2 is the X-ray diffraction pattern of the LTA-type molecular sieve prepared in Example 1.

[0035] Figure 3 is a scanning electron microscope image of the LTA molecular sieve prepared in Example 1.

[0036] Figure 4 shows the X-ray diffraction pattern of the FAU-type molecular sieve prepared in Example 2.

[0037] Figure 5 shows the X-ray diffraction pattern of the SOD-type molecular sieve prepared in Example 3.

[0038] Figure 6 shows the X-ray diffraction pattern of the LTN molecular sieve prepared in Example 4.

[0039] Figure 7 shows the X-ray diffraction pattern of the LTA-type molecular sieve prepared in Comparative Example 5.

[0040] Figure 8 shows the X-ray diffraction pattern of the LTA-type molecular sieve prepared in Comparative Example 6.

[0041] Figure 9 shows the X-ray diffraction pattern of the LTA-type molecular sieve prepared in Comparative Example 7. Detailed Implementation

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0045] Example 1

[0046] A method for preparing LTA-type molecular sieves based on fly ash includes the following steps:

[0047] (1) 10g of fly ash and 5g of sodium hydroxide were activated by ball milling. After ball milling at 200℃ for 3h, the mixture was transferred to a stainless steel container and 300mL of 2.4mol / L sodium hydroxide aqueous solution was added to obtain mixed solution I.

[0048] (2) Add diesel fuel to the mixed solution I in step (1), introduce nitrogen gas to foam, separate the suspended foam, and obtain mixed solution II.

[0049] (3) Heat the mixed solution II in step (2) at 80℃ and stir vigorously for 2 hours to obtain mixed solution III.

[0050] (4) The mixed solution III from step (3) was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis reactor and crystallized at 100°C for 3 hours. After the hydrothermal synthesis reactor cooled to room temperature, the product was filtered dry, and water was added at 50°C to slurry for 20 minutes. Solid-liquid separation was then performed, and the resulting solid was dried at 105°C for 12 hours to obtain the LTA-type molecular sieve.

[0051] The X-ray diffraction pattern of fly ash in Example 1 is shown in Figure 1. The X-ray diffraction pattern of LTA molecular sieve prepared in Example 1 is shown in Figure 2. The product conforms to the peak characteristics of LTA molecular sieve. The scanning electron microscope image of LTA molecular sieve prepared in Example 1 is shown in Figure 3.

[0052] Example 2

[0053] A method for preparing FAU-type molecular sieves based on fly ash includes the following steps:

[0054] (1) 10g of fly ash and 10g of potassium hydroxide were activated by ball milling. After ball milling at 150℃ for 6h, the mixture was transferred to a stainless steel container and 200mL of 3.2mol / L sodium hydroxide aqueous solution was added to obtain mixed solution I.

[0055] (2) Add pine oil to the mixed solution I in step (1), introduce air to foam, separate the suspended foam, and obtain mixed solution II.

[0056] (3) Add 12g of sodium silicate to mixed solution II, heat at 90℃ and stir vigorously for 4h to obtain mixed solution III.

[0057] (4) The mixed solution III from step (3) was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis reactor and crystallized at 105°C for 14 hours. After the hydrothermal synthesis reactor cooled to room temperature, the product was filtered dry, and water was added at 40°C to slurry the mixture for 30 minutes. Solid-liquid separation was then performed, and the resulting solid was dried at 80°C for 16 hours to obtain the FAU-type molecular sieve.

[0058] The X-ray diffraction pattern of the FAU-type molecular sieve prepared in Example 2 is shown in Figure 4. The product conforms to the peak characteristics of FAU-type molecular sieve.

[0059] Example 3

[0060] A method for preparing SOD-type molecular sieves based on fly ash includes the following steps:

[0061] (1) 10g of fly ash and 8g of sodium hydroxide were activated by ball milling. After ball milling at 175℃ for 4h, the mixture was transferred to a stainless steel container and 200mL of 2.8mol / L sodium hydroxide aqueous solution was added to obtain mixed solution I.

[0062] (2) Add diesel fuel to the mixed solution I in step (1), introduce air to foam, separate the suspended foam, and obtain mixed solution II.

[0063] (3) Heat the mixed solution II in step (2) at 80℃ and stir vigorously for 4 hours to obtain mixed solution III.

[0064] (4) The mixed solution III from step (3) was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis reactor and crystallized at 105°C for 12 hours. After the hydrothermal synthesis reactor cooled to room temperature, the product was filtered dry, and water was added at 30°C to slurry the mixture for 50 minutes. Solid-liquid separation was then performed, and the resulting solid was dried at 100°C for 12 hours to obtain the SOD-type molecular sieve.

[0065] The X-ray diffraction pattern of the SOD-type molecular sieve prepared in Example 3 is shown in Figure 5. The product conforms to the peak characteristics of SOD-type molecular sieve.

[0066] Example 4

[0067] A method for preparing LTN-type molecular sieves based on fly ash includes the following steps:

[0068] (1) 10g fly ash, 12g sodium hydroxide and 3g potassium hydroxide were activated by ball milling. After ball milling at 200℃ for 3h, the mixture was transferred to a stainless steel container and 200mL of 3.6mol / L sodium hydroxide aqueous solution was added to obtain mixed solution I.

[0069] (2) Add diesel fuel to the mixed solution I in step (1), introduce air to foam, separate the suspended foam, and obtain mixed solution II.

[0070] (3) Heat the mixed solution II in step (2) at 70℃ and stir vigorously for 6 hours to obtain mixed solution III.

[0071] (4) The mixed solution III from step (3) was transferred to a polytetrafluoroethylene-lined hydrothermal synthesis reactor and crystallized at 100°C for 2 hours. After the hydrothermal synthesis reactor cooled to room temperature, the product was filtered dry, and water was added at 60°C to slurry the mixture for 15 minutes. Solid-liquid separation was then performed, and the resulting solid was dried at 110°C for 10 hours to obtain the LTN-type molecular sieve.

[0072] The X-ray diffraction pattern of the LTN molecular sieve prepared in Example 4 is shown in Figure 6. The product conforms to the peak characteristics of LTN molecular sieve.

[0073] Comparative Example 1

[0074] A method for preparing LTA-type molecular sieve based on fly ash (CN104843735A) includes the following steps: mixing magnetically separated fly ash with sodium carbonate, calcining at high temperature and then grinding, washing with water to remove silicon, and using the filtrate and filter residue after washing as raw materials to synthesize LTA-type molecular sieve.

[0075] This method involves alkaline fusion activation of fly ash at 700–800℃, which results in high energy consumption. Furthermore, the method adjusts the silica-alumina ratio of fly ash through water washing and desilication, making the process cumbersome. The desilication process requires a large amount of water for rinsing, increasing waste liquid production and making industrial-scale production difficult.

[0076] Comparative Example 2

[0077] A method for preparing FAU-type molecular sieve based on fly ash (CN106865565A) includes the following steps: calcining fly ash to remove carbon, acid washing to remove impurities such as metal oxides, and then mixing and reacting it with sodium hydroxide solution to synthesize FAU-type molecular sieve.

[0078] This method requires calcination at 550–850℃ to remove carbon, which is difficult to achieve industrially and has high energy consumption, making it unsuitable for industrial production. Furthermore, while removing impurities through acid leaching, this method fails to fully activate the fly ash and generates a large amount of acidic waste liquid, which is difficult to treat later.

[0079] Comparative Example 3

[0080] A method for preparing SOD-type molecular sieve based on fly ash (CN10364113A) includes the following steps: washing fly ash with clean water and drying it, mixing it with sodium hydroxide solution and transferring it to a high-pressure reaction device, reacting it at a constant temperature for a period of time to synthesize SOD-type molecular sieve.

[0081] This method removes impurities from fly ash by washing with water, but it is difficult to completely remove light, insoluble carbon. Furthermore, the raw fly ash is not activated, resulting in low utilization of silicon and aluminum elements and poor crystallinity of the product.

[0082] Comparative Example 4

[0083] A method for preparing SOD-type molecular sieve based on fly ash (CN109095476A) includes the following steps: mixing fly ash with a high-concentration sodium hydroxide solution and reacting under high temperature and high pressure conditions of not less than 220℃ to synthesize SOD-type molecular sieve.

[0084] This method requires reaction under high temperature and high pressure conditions of no less than 220℃, which is difficult to achieve industrially. In addition, the fly ash raw material in this method is not decarbonized, resulting in the crystallinity of the SOD-type molecular sieve product being concentrated at around 90%, making it difficult to further improve the crystallinity.

[0085] Comparative Example 5

[0086] A method for preparing LTA-type molecular sieves based on fly ash is basically the same as that in Example 1, except that 5g of sodium hydroxide is not added during the activation process.

[0087] Because this method does not add alkaline compounds, ball milling only reduces the particle size of fly ash. The inert components such as quartz and mullite in the fly ash are not fully activated. When heated with alkaline water, the silicon and aluminum elements in the fly ash are difficult to dissolve, resulting in low utilization of silicon and aluminum in the raw materials and poor crystallinity of the product.

[0088] The X-ray diffraction pattern of the LTA-type molecular sieve prepared in Comparative Example 5 is shown in Figure 7. The product conforms to the peak characteristics of LTA-type molecular sieve.

[0089] Comparative Example 6

[0090] A method for preparing LTA-type molecular sieves based on fly ash is basically the same as that in Example 1, except that 300 mL of 2.4 mol / L sodium hydroxide aqueous solution is replaced with 300 mL of deionized water.

[0091] Because this method does not include an alkaline solution, the alkalinity of mixed solution I is too low, resulting in insufficient dissolution of silicon and aluminum elements from the raw materials. The undissolved silicon and aluminum compounds act as impurities during the synthesis of molecular sieves, leading to poor crystallinity in the product.

[0092] The X-ray diffraction pattern of the LTA-type molecular sieve prepared in Comparative Example 6 is shown in Figure 8. The product basically conforms to the peak characteristics of LTA-type molecular sieve.

[0093] Comparative Example 7

[0094] A method for preparing LTA molecular sieve based on fly ash is basically the same as that in Example 1, except that the flotation operation in step (2) is not performed.

[0095] Because this method does not involve flotation, the mixed solution II contains a large number of light, insoluble impurities, resulting in a significant decrease in the crystallinity of the product.

[0096] The X-ray diffraction pattern of the LTA-type molecular sieve prepared in Comparative Example 7 is shown in Figure 9. The product basically conforms to the peak characteristics of LTA-type molecular sieve.

[0097] The relative crystallinity of Examples 1-4 and Comparative Examples 1-7 was calculated using the following formula:

[0098]

[0099] Where X c X0 represents the relative crystallinity of the synthesized product, in %; X0 represents the crystallinity of the molecular sieve standard of this type, in %; I c Ikl represents the diffraction intensity of a certain crystal plane (hkl) of the synthesized product; I0 represents the diffraction intensity of a certain crystal plane (hkl) of the molecular sieve standard of this type.

[0100] The relative crystallinity data of Examples 1-4 and Comparative Examples 1-7 are shown in Table 1:

[0101] Table 1

[0102]

[0103] As can be seen from Table 1, the SOD-type molecular sieves based on fly ash prepared by the method provided in this invention have higher crystallinity than those prepared by currently disclosed methods, indicating that this invention can effectively improve the crystallinity of the synthesized SOD-type molecular sieves. Furthermore, Comparative Examples 5-7 demonstrate that the preparation method of this invention can effectively activate fly ash, improve the utilization rate of silicon and aluminum oxides in fly ash, and efficiently remove light, insoluble impurities from fly ash.

[0104] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing SOD-type molecular sieves based on fly ash, characterized in that, Includes the following steps: (1) Fly ash and alkaline compounds are activated by ball milling or grinding at 50~200 ℃, and mixed solution I is obtained after adding alkaline solution; the mass ratio of fly ash and alkaline compound is 1:(0.5~50); the solid-liquid ratio of mixed solution I is 1:(10~50) g / mL; the concentration of alkaline solution is 0.5~10 mol / L; (2) Flotation agent is added to mixed solution I in step (1), gas is introduced for foaming, and suspended foam is separated to obtain mixed solution II; (3) Mixed solution II in step (2) is heated to obtain mixed solution III; (4) Mixed solution III in step (3) is crystallized, water is added for slurrying and solid-liquid separation is performed, and the obtained solid is dried to obtain the SOD molecular sieve.

2. The preparation method according to claim 1, characterized in that, In step (1), the alkaline compound is selected from one or more of alkali metal oxides, alkali metal hydroxides, alkaline earth metal oxides and alkaline earth metal hydroxides, and the alkaline solution is an aqueous solution of alkali metal hydroxide and / or an aqueous solution of alkaline earth metal hydroxide.

3. The preparation method according to claim 1, characterized in that, In step (2), the flotation agent is selected from one or more of oleic acid, kerosene, diesel oil, pine oil and 2-octanol, and the gas is air and / or an inert gas.

4. The preparation method according to claim 1, characterized in that, In step (3), the heating temperature is 60~100 ℃ and the heating time is 0.5~16 h.

5. The preparation method according to claim 1, characterized in that, In step (3), the process of replenishing silicon and / or aluminum sources before heating is also included.

6. The preparation method according to claim 1, characterized in that, In step (4), the temperature of the crystallization treatment is 25~220 ℃ and the time of the crystallization treatment is 1~72 h.

7. The preparation method according to any one of claims 1 to 6, characterized in that, In step (4), the skeleton type of the SOD molecular sieve is LTA, FAU, SOD, LTN, EMT, FAR, GIU, MAR, TSC or FRA.

8. The fly ash-based SOD molecular sieve prepared by the method according to any one of claims 1 to 7.

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