Silanization modified X-type molecular sieve based on fly ash as well as preparation method and application of silanization modified X-type molecular sieve

Abstract

The invention discloses a coal ash-based silanization modified X-type molecular sieve as well as a preparation method and application thereof, and relates to the technical field of molecular sieve preparation. Mixing a silanization reagent with an organic reagent to obtain a mixed solution; mixing the X-type molecular sieve with the mixed solution, heating, and carrying out condensation reflux to obtain a silanization modified X-type molecular sieve crude product; and centrifuging, washing, aging and calcining the silanization modified X-type molecular sieve crude product to obtain the silanization modified X-type molecular sieve. The coal ash resource can be efficiently utilized, the service life of the molecular sieve is prolonged, and meanwhile, the molecular sieve has efficient carbon dioxide catalytic adsorption performance.

Description

Technical Field

[0001] The present invention relates to a silanized modified X-type molecular sieve based on fly ash, its preparation method and application, belonging to the technical field of molecular sieve preparation. Background Art

[0002] As the main industrial waste discharged from coal-fired power plants, fly ash mainly consists of silicon dioxide and alumina, and has the characteristic of a high silicon-aluminum ratio. Traditional fly ash treatment methods include landfill and stacking, etc., which not only occupy a large amount of land resources, but may also cause secondary pollution to the environment. Therefore, how to efficiently utilize the silicon-aluminum resources in fly ash is one of the current research hotspots. It has important practical significance to convert fly ash into materials with high added value, especially to apply it as an adsorbent material in the field of environmental protection.

[0003] As industrial waste gas, flue gas mainly contains carbon dioxide (CO2), nitrogen (N2), oxygen (O2) and a small amount of pollutants such as sulfides and nitrogen oxides. Among them, as the main greenhouse gas, the large emission of carbon dioxide has a profound impact on global climate change. Traditional carbon dioxide capture methods often face problems such as high energy consumption, low efficiency and acid gas corrosion. Acid gas corrosion not only affects the service life of the capture equipment, but also reduces the capture efficiency and increases the operating cost. Therefore, developing an efficient, low-cost and corrosion-resistant adsorbent material to achieve efficient adsorption and capture of carbon dioxide has become the research focus of current environmental protection technologies.

[0004] Molecular sieve is a new type of porous material with excellent adsorption performance. In the aspect of carbon dioxide capture, molecular sieve shows good prospects. However, the existing molecular sieve preparation process is relatively complex and the cost is relatively high, which limits its large-scale application. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a silanized modified X-type molecular sieve based on fly ash, its preparation method and application, which can efficiently utilize fly ash resources, improve the service life of the molecular sieve and make it have high-efficiency carbon dioxide catalytic adsorption performance.

[0006] To achieve the above purpose, the present invention is implemented by the following technical solutions: In the first aspect, the present invention provides a preparation method of a silanized modified X-type molecular sieve based on fly ash, including: Preparing an X-type molecular sieve using fly ash; Mixing a silanizing reagent and an organic reagent to obtain a mixed solution; Mixing the X-type molecular sieve with the mixed solution, performing condensation reflux after reaction, and obtaining a crude product of the silanized modified X-type molecular sieve; The crude product of silanized X-type molecular sieve is centrifuged, washed, aged, and calcined to obtain the silanized X-type molecular sieve.

[0007] Further, the preparation of X-type molecular sieve using fly ash includes: Mix fly ash and an alkali source to obtain a fly ash mixture; Add water to the fly ash mixture to obtain a mixed solution, and after crystallization treatment, dry it to obtain X-type molecular sieve; Among them, the crystallization treatment includes putting the mixed solution into a reaction kettle, and placing the reaction kettle in a constant temperature oven to keep at 90 - 120 °C for 3 - 5 days.

[0008] Further, the alkali source is one of sodium hydroxide, ammonia water, and sodium carbonate.

[0009] Further, the volume ratio of the silanizing reagent to the organic solvent is 1:100 - 250.

[0010] Further, the silanizing reagent is one of trichloromethylsilane, trimethylchlorosilane, and allyltriethoxysilane; and / or, the organic solvent is toluene or o-xylene.

[0011] Further, the mass ratio of the X-type molecular sieve to the silanizing reagent is 10 - 50:1.

[0012] Further, at least one of the following conditions is satisfied: The reaction temperature range is 60 - 120 °C; The condensation reflux time is 3 - 12 h; The condition parameters of the centrifugation include centrifuging at a speed of 10000 rpm for 40 - 80 min; The number of washing times is 6 - 12 times; The aging time is 12 - 36 h; The calcination includes placing it in a muffle furnace and calcining at 550 - 650 °C for 6 - 10 h.

[0013] In the second aspect, the present invention provides a silanized X-type molecular sieve, which is prepared by the preparation method of the silanized X-type molecular sieve based on fly ash as described in any one of the above.

[0014] In the third aspect, the present invention further provides an application of the silanized X-type molecular sieve as described above in carbon dioxide catalysis and carbon dioxide adsorption.

[0015] Further, the reaction condition parameters of the carbon dioxide catalysis include: the temperature is 300 - 700 °C, the reaction pressure is 2 - 10 MPa, and the gas flow rate is 10 - 200 mL / min.

[0016] Advantages achieved by the present invention compared with the prior art: In the present invention, silane groups (such as chlorosilane, alkylsilane, etc.) are introduced onto the surface of the molecular sieve through silanization modification. The silane groups can enhance the chemical stability of the molecular sieve. The surface of the silanized modified molecular sieve is protected and can withstand more severe reaction conditions; moreover, silanization modification can improve the pore structure of the molecular sieve, making its porosity and pore size distribution more uniform, which helps to increase the adsorption capacity of carbon dioxide. A more uniform pore size distribution is conducive to the diffusion and adsorption process of carbon dioxide molecules in the pores of the molecular sieve, thereby improving the adsorption efficiency. The polarity and electronic effects of the organic groups introduced by silanization enable it to have a stronger interaction with CO2 molecules. For example, certain silane groups (such as nitrogen-containing groups) can form strong physical adsorption or chemical adsorption with CO2, thus increasing the adsorption capacity; silanization modification makes X-type molecular sieves generally have better thermal stability and regeneration performance. During the adsorption-desorption process of carbon dioxide, silanization modification can reduce the damage to the molecular sieve structure, thereby ensuring that it can still maintain a high adsorption effect during multiple cycles of use. This is very important for long-term operations such as CO2 capture in practical applications.

[0017] The silanized modified X-type molecular sieve prepared by the present invention can maintain good stability and regeneration performance under harsh conditions such as high temperature and high humidity, and at the same time has good acid corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the X-ray diffraction pattern of the silanized modified X-type molecular sieve prepared in Example 1 of the present invention; Figure 2 Schematic diagram of the X-ray diffraction pattern before and after acid leaching test of the silanized modified X-type molecular sieve prepared in Example 1 of the present invention and the commercial X-type molecular sieve of the comparative example; Figure 3 SEM scanning electron microscope schematic diagram of the silanized modified X-type molecular sieve prepared in Example 1 of the present invention after acid leaching test; Figure 4 SEM scanning electron microscope schematic diagram of the silanized modified X-type molecular sieve prepared in Example 1 of the present invention before acid leaching test. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be further described below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention. Example 1

[0020] An embodiment of the present invention provides a method for preparing a silanized modified X-type molecular sieve. The preparation method is based on fly ash and specifically includes the following steps: First, prepare the X-type molecular sieve: Mix fly ash and sodium hydroxide in a volume ratio of 1:10 to obtain a fly ash mixture. Mix the fly ash mixture with water, add it to a reaction kettle, place the reaction kettle in a constant-temperature oven, and keep it at 120 °C for 3 days for crystallization treatment. Put the product after crystallization treatment into a muffle furnace and dry it at 600 °C to obtain the X-type molecular sieve.

[0021] Then, mix 0.2 mL of allyltriethoxysilane with 50 mL of toluene to form a mixture. Toluene, as a typical non-polar solvent, has strong dissolving ability and can effectively dissolve the organic part (such as ethoxy and allyl) of allyltriethoxysilane, ensuring the dispersibility and uniformity of the silanization reagent during the reaction, avoiding the over-aggregation or precipitation of the silanization reagent, and thus avoiding unnecessary side reactions and material waste. At the same time, toluene has low volatility, which means it can maintain a stable temperature environment during the reaction, prevent the premature volatilization of the solvent or other side reactions, and contribute to improving the controllability and stability of the reaction.

[0022] Next, gradually add the X-type molecular sieve to the mixture, and control the mass ratio of allyltriethoxysilane to the X-type molecular sieve to be 1:10. The full contact between the mixture and the X-type molecular sieve helps the allyltriethoxysilane molecules to attach to the pores of the X-type molecular sieve to form a silanized product.

[0023] Heat the silanized product at 80 °C and carry out a 3-hour condensation reflux reaction to ensure the full progress of the reaction. At this temperature, the reaction occurs between allyltriethoxysilane and the surface of the X-type molecular sieve, and the silanization reaction reaches the expected effect. Condensation reflux can not only keep the reactants at a constant temperature, but also increase the concentration of the reaction substances, promote the dissolution and migration of the reaction substances, and thus improve the reaction efficiency.

[0024] After the reaction is completed, in order to remove the residual toluene in the reaction system, perform high-speed centrifugation at 10000 r for 50 minutes to ensure the removal of most of the impurities and residual solvents, wash with ethanol, and then carry out an aging treatment for 12 h to make its structure more stable. Aging can promote the crystallization of the product, remove unnecessary stress, make the crystals more perfect, and improve the stability of the pore structure of the X-type molecular sieve.

[0025] Finally, put the product into a muffle furnace and calcine it at 550 °C for 6 h to obtain the silanized modified X-type molecular sieve.

[0026] The main function of calcination is to improve the crystallinity and structural stability of the molecular sieve, while removing residual organic matter and insoluble substances. By heating, the silicon-aluminum framework in the molecular sieve rearranges, promoting the orderly arrangement of the framework and improving the crystal integrity. During this process, the pore structure of the molecular sieve is optimized, the pore diameter and pore volume are improved, thus significantly enhancing its performance in catalytic reactions. At a high temperature of 550 °C, calcination helps to optimize the distribution of acidic sites in the molecular sieve, enhance its acidity and surface structure, making it more suitable for catalytic applications. The acidic sites of the molecular sieve will redistribute during this process, having higher catalytic activity, especially in the catalytic reaction of flue gas adsorption, which can improve the efficiency and selectivity of the catalytic reaction. In addition, calcination at 550 °C can further improve the thermal stability of the molecular sieve, enabling it to maintain high stability in a high-temperature reaction environment and not easily undergo structural damage.

[0027] The X-ray diffraction pattern of the silanized modified X-type molecular sieve prepared in this example is as Figure 1 shown. Combining Figure 1 , the peak shape of the XRD peaks of the silanized modified X-type molecular sieve is sharper, indicating that the molecular sieve has higher crystallinity. Example 2

[0028] This example provides a preparation method of a silanized modified X-type molecular sieve, which is only different from Example 1 in that 0.2 mL of trichloromethylsilane is mixed with 50 mL of toluene to form a mixed solution. Example 3

[0029] This example provides a preparation method of a silanized modified X-type molecular sieve, which is only different from Example 1 in that the mass ratio of allyltriethoxysilane to the X-type molecular sieve is controlled to be 1:40. Example 4

[0030] This example provides a preparation method of a silanized modified X-type molecular sieve, which is only different from Example 1 in that the silanizing agent is heated and reacted at 80 °C and subjected to a 6-hour condensation reflux reaction. Example 5

[0031] This example provides a preparation method of a silanized modified X-type molecular sieve, which is only different from Example 1 in that the product is placed in a muffle furnace and calcined at 550 °C for 10 h. Example 6

[0032] This example provides a preparation method of a silanized modified X-type molecular sieve, which is only different from Example 1 in that 0.2 mL of allyltriethoxysilane is mixed with 20 mL of toluene to form a mixed solution.

[0033] Comparative example: This comparative example uses unmodified 13X zeolite molecular sieve, purchased from Tianjin Nanhua Catalyst Co., Ltd., denoted as commercial X-type molecular sieve.

[0034] Next, the silanized modified X-type molecular sieve prepared in Example 1 and the commercial X-type molecular sieve in the comparative example were subjected to an acid solution immersion test. The test method is as follows: 10 g of the silanized modified X-type molecular sieve prepared in Example 1 and 10 g of the commercial X-type molecular sieve in the comparative example were respectively taken and added to 100 mL of 1 mol / L sulfuric acid solution. After standing for 12 h, they were taken out to obtain the acid-leached product of the silanized modified X-type molecular sieve and the acid-leached product of the commercial X-type molecular sieve.

[0035] X-ray diffraction tests were carried out on the acid-leached product of the silanized modified X-type molecular sieve, the acid-leached product of the commercial X-type molecular sieve, and the product of the commercial X-type molecular sieve before acid leaching, as shown in Figure 2 shown.

[0036] Combined with Figure 1 and Figure 2 it can be seen that after long-term acid leaching, the XRD peaks of the silanized modified X-type molecular sieve did not change significantly, while obvious spectral line shifts occurred in the commercial X-type molecular sieve before and after acid leaching. This effectively shows that the acid corrosion resistance of the silanized modified X-type molecular sieve is better than that of the commercial X-type molecular sieve, and the silanized modified X-type molecular sieve has good acid corrosion resistance.

[0037] Furthermore, 10 g of the silanized modified X-type molecular sieve prepared in Example 1 was taken for SEM testing. The test condition parameters were that the acceleration voltage of the electron beam was set to 5 kV, the working distance between the sample and the electron gun was 10.1 mm, the magnification was 20,000 times, and the secondary electron detection mode was used to obtain Figure 4 . Then it was added to 100 mL of 1 mol / L sulfuric acid solution and left standing for 12 h. After taking it out, SEM testing was carried out again. The test condition parameters were that the acceleration voltage of the electron beam was set to 5 kV, the working distance between the sample and the electron gun was 10.1 mm, the magnification was 18,000 times, and the secondary electron detection mode was used to obtain Figure 3 .

[0038] From Figure 3 and Figure 4 it can be seen that after 12 hours of strong acid immersion, the crystal surface of the silanized modified X-type molecular sieve is flat and the structure is complete, and the regular octahedral morphology has not changed significantly, indicating that the silanized modified X-type molecular sieve has good acid corrosion resistance.

[0039] The silanized modified X-type molecular sieves prepared in Examples 1-6 and the commercial X-type molecular sieves prepared in the comparative example were used for carbon dioxide catalytic adsorption. The reaction conditions were a temperature of 30 °C and a reaction pressure of 300 kPa. The carbon dioxide adsorption capacities are shown in Table 1.

[0040] Table 1: Carbon dioxide adsorption capacity results of the silanized modified X-type molecular sieves prepared in Examples 1-6 and the commercial X-type molecular sieves prepared in the comparative example

[0041] As can be seen from Table 1, the carbon dioxide adsorption effect of the unmodified X-type molecular sieve in the comparative example is significantly worse than that of the examples of the present invention. From the results of Examples 1-6, it can be seen that an appropriate increase in the calcination time is beneficial to the improvement of the carbon dioxide adsorption effect, and an increase in the proportion of the silanization reagent in the mixed solution within a certain range also helps to improve the carbon dioxide adsorption effect.

[0042] This is because: the silanization modification of the present invention can introduce silyl groups (such as chlorosilane, alkylsilane, etc.) on the surface of the molecular sieve, and these silyl groups can enhance the chemical stability of the molecular sieve. Ordinary X-type molecular sieves are easily damaged in acidic or alkaline environments, while after silanization modification, the surface is protected and can withstand more severe reaction conditions. The silanization modification can improve the pore structure of the molecular sieve, making its porosity and pore size distribution more uniform, which helps to improve the carbon dioxide adsorption capacity. A more uniform pore size distribution helps the diffusion and adsorption process of carbon dioxide molecules in the molecular sieve pores, thereby improving the adsorption efficiency. The polarity and electronic effect of the organic groups introduced by silanization enable it to have a stronger interaction with CO2 molecules. For example, certain silyl groups (such as nitrogen-containing groups) can form strong physical adsorption or chemical adsorption with CO2, thereby increasing the adsorption capacity.

[0043] The silanized modified X-type molecular sieve usually has better thermal stability and regeneration performance. During the carbon dioxide adsorption-desorption process, the silanization modification can reduce the damage to the molecular sieve structure, so as to ensure that it can still maintain a high adsorption effect during multiple cycles of use. This is very important for long-term operations such as CO2 capture in practical applications.

[0044] When X-type molecular sieve adsorbs carbon dioxide, if there is moisture, it may affect the carbon dioxide adsorption capacity and rate. The silanization treatment can effectively reduce the influence of moisture, especially in humid or high-humidity environments, enhancing the efficiency and stability of the molecular sieve during carbon dioxide adsorption. And through silanization modification, the adsorption selectivity of X-type molecular sieve for carbon dioxide can be further optimized. For example, after modification, it may be able to better inhibit the competitive adsorption of other gases such as nitrogen and oxygen, selectively adsorb carbon dioxide, and increase its application effect in gas separation or capture.

[0045] In summary, compared with ordinary X-type molecular sieves, the silylated modified X-type molecular sieves exhibit better chemical stability, higher adsorption capacity, stronger adsorption affinity and better regeneration performance during the catalytic adsorption process of carbon dioxide. Therefore, they have greater application potential in aspects such as CO2 capture, separation and gas purification.

[0046] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of silanized modified X-type zeolite based on fly ash, characterized in that, Including: Preparing X-type molecular sieve using fly ash; Mixing a silanizing reagent and an organic reagent to obtain a mixed solution; Mixing the X-type molecular sieve with the mixed solution, carrying out condensation reflux after reaction to obtain a crude product of silanized modified X-type molecular sieve; Centrifuging, washing, aging, and calcining the crude product of silanized modified X-type molecular sieve to obtain the silanized modified X-type molecular sieve.

2. The preparation method of the silanized modified X-type molecular sieve based on fly ash according to claim 1, characterized in that, The preparation of the X-type molecular sieve using fly ash includes: Mixing fly ash and an alkali source to obtain a fly ash mixed solution; Adding water to the fly ash mixed solution to obtain a mixed solution, drying after crystallization treatment to obtain the X-type molecular sieve; Among them, the crystallization treatment includes putting the mixed solution into a reaction kettle, and placing the reaction kettle in a constant temperature oven to keep at 90 - 120 °C for 3 - 5 days.

3. The preparation method of the silanized modified X-type molecular sieve based on fly ash according to claim 2, characterized in that, The alkali source is one of sodium hydroxide, ammonia water, and sodium carbonate.

4. The preparation method of the silanized modified X-type molecular sieve based on fly ash according to claim 1, characterized in that, The volume ratio of the silanizing reagent to the organic solvent is 1:100 - 250.

5. The preparation method of the silanized modified X-type molecular sieve based on fly ash according to claim 4, wherein, The silanizing reagent is one of trichloromethylsilane, trimethylchlorosilane, and allyltriethoxysilane; and / or, the organic solvent is toluene or o-xylene.

6. The preparation method of the silanized modified X-type molecular sieve based on fly ash according to claim 1, wherein, The mass ratio of the X-type molecular sieve to the silanizing reagent is 10 - 50:

1.

7. The preparation method of the silanized modified X-type molecular sieve based on fly ash according to claim 1, characterized in that, At least one of the following conditions is satisfied: The reaction temperature range is 60 - 120 °C; The condensation reflux time is 3 - 12 hours; The condition parameters of the centrifugation include centrifuging at 10000 rpm for 40 - 80 min; The number of washing times is 6 - 12 times; The aging time is 12 - 36 h; The calcination includes calcining in a muffle furnace at 550 - 650 °C for 6 - 10 h.

8. A silanized modified X-type molecular sieve, characterized in that, Prepared by the preparation method of the silanized modified X-type molecular sieve based on fly ash according to any one of claims 1 - 7.

9. An application of the silanized modified X-type molecular sieve according to claim 8 in carbon dioxide catalysis and carbon dioxide adsorption.

10. The application according to claim 9, wherein The reaction condition parameters of the carbon dioxide catalysis include: the temperature is 300 - 700 °C, the reaction pressure is 2 - 10 MPa, and the gas flow rate is 10 - 200 mL / min.

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