Method for preparing solid waste silicon-based composite oxide aerogel

Abstract

The invention discloses a method for preparing solid waste silicon-based composite oxide aerogel by taking bulk solid waste as a silicon source, providing other oxide components with inorganic salt and combining a sol-gel method and a normal-pressure drying method, which comprises the following steps: uniformly mixing the bulk solid waste and alkaline solid powder, and calcining to obtain the solid waste silicon-based composite oxide aerogel. The preparation method comprises the following steps: preparing a sintering material, dissolving the sintering material by using a dilute acid solution, filtering to obtain a silicon precursor, adding the silicon precursor into a precursor prepared by taking inorganic salt as an oxide component, then adding epoxypropane as a coagulant to obtain silicon-based wet gel, then carrying out solvent replacement and surface modification, and finally carrying out normal-pressure drying to obtain the silicon-based composite oxide aerogel. According to the preparation method, a large amount of solid waste is taken as a raw material to replace a traditional expensive organic silicon source, a normal pressure drying mode is adopted, so that the preparation process is simple and safe, the production cost is greatly reduced, the silicon-based composite oxide aerogel is obtained by compounding the inorganic salt, and the high temperature resistance and heat insulation performance of the pure SiO2 aerogel are improved.

Description

Technical Field:

[0001] The present invention belongs to the field of preparation processes of aerogel materials, and relates to a method for preparing a silicon-based composite oxide aerogel, in particular to a method for preparing a waste silicon-based composite oxide aerogel by combining a sol-gel method with an atmospheric pressure drying method, using bulk solid waste as a silicon source and inorganic salts to provide other oxide components. Background Art:

[0002] As a new type of thermal protection material, aerogel has a continuous three-dimensional nano-porous network structure, endowing it with characteristics such as ultra-low density, high specific surface area, and high porosity. The unique network structure of aerogel can effectively limit heat transfer, inhibit convective heat transfer of gas molecules and solid heat conduction, and the pore structure of aerogel can be microscopically regulated through the sol-gel process. Therefore, aerogel is considered an ideal high-efficiency thermal protection material, with a thermal conductivity lower than that of still air at room temperature, far superior to traditional thermal insulation materials, and thus is known as the "super thermal insulation material".

[0003] SiO 2 Silica aerogel is the earliest and most technically mature material in the field of aerogel materials. Due to its unique three-dimensional porous structure, low density, high porosity, etc., it has broad application prospects in many fields. Although silica aerogel has excellent thermal insulation performance, at high temperatures, the nanoparticles inside the aerogel may sinter, resulting in the collapse of the pore structure, an increase in density, and thus a sharp rise in thermal conductivity, losing the lightweight and porous characteristics of aerogel, leading to disadvantages such as poor high-temperature thermal stability. To improve the temperature resistance of silica aerogel, researchers have adopted various strategies, including introducing different oxide components to inhibit its phase transition process at high temperatures, such as ZrO 2 -SiO 2 、Al 2 O 3 -SiO 2 and CeO 2 -SiO 2 etc. Wang et al. (Journal of sol-gel science and technology, 2018, 87: 734 - 742.) developed a new "thiol-ene" reaction route to synthesize ZrO 2 -SiO 2 aerogel. The basic principle is to use SiO 2 to modify the ZrO 2 main chain, which is an effective way to improve the strength and thermal stability of aerogel. The composite aerogel obtained by this method has better thermal stability and still maintains a high specific surface area even at a temperature of 1000°C. In addition, some researchers have carried out research on SiO 2and Al 2 O 3 Based on this, a binary Al 2 O 3 -SiO 2 aerogel was developed. Silicon atoms are easily filled into the cation vacancies of alumina. After these vacancies are filled, the surface diffusion of silicon atoms can be well inhibited. At the same time, the double-network structure effectively increases the diffusion paths of silicon and oxygen atoms, increases the free energy required for the transformation from the amorphous state to the crystalline state, and can also inhibit the phase change of Al 2 O 3 at high temperatures, thereby improving the temperature resistance of the overall material. Ocejo, Marta et al. (Materials Chemistry and Physics, 2024, 303: 124425.) prepared Al 2 O 3 -SiO 2 aerogel, and prepared low-density and high-temperature-resistant Al 2 O 3 -SiO 2 aerogel by adjusting the aluminum-silicon ratio. After heat treatment at 1200 °C, the sample still has a high specific surface area. At present, the raw materials for preparing SiO 2 aerogel mainly include organosilicon sources such as tetraethyl orthosilicate and methyl orthosilicate. They are hydrolyzed under acidic conditions and induced to condense Si-OH to form a three-dimensional network structure in the shape of a "pearl chain" under alkaline conditions. Although the performance is improved after adding tetraethyl orthosilicate, the production cost is greatly increased.

[0004] Therefore, there is an urgent need to develop a method for preparing polybornite composite oxide aerogel materials from bulk solid wastes, which can not only reduce the production cost of aerogel materials, achieve the effect of cost reduction and efficiency increase, but also realize good resource utilization, and is of great significance to the sustainable development of mineral resources. Summary of the Invention:

[0005] The purpose of the present invention is to provide a method for preparing solid waste silicon-based composite oxide aerogel to improve the deficiencies existing in the prior art. Using bulk solid wastes as raw materials not only reduces the raw material cost of aerogel, but also improves the utilization efficiency of bulk solid wastes and realizes resource utilization. Through the atmospheric drying process, silicon-based composite oxide aerogel is prepared, which has low cost, simple process, safe operation, good controllability of the microstructure. The prepared aerogel particles have a large specific surface area and an extremely low thermal conductivity, and have excellent high-temperature heat insulation performance, which has positive production significance for realizing the application of aerogel materials in multiple fields such as environmental protection, energy conservation, chemical engineering, and aviation.

[0006] The purpose of the present invention is achieved through the following technical solutions: A method for preparing solid waste silicon-based composite oxide aerogel, and its specific steps are as follows:

[0007] (1) Crush and grind the solid waste raw materials and screen them to 100 - 800 mesh to obtain the pre-treated powder.

[0008] (2) Uniformly mix the pre-treated powder with the alkaline solid powder and put it into a muffle furnace for high-temperature calcination to obtain the activated powder.

[0009] (3) Grind the activated powder and add it to the dilute acid solution in proportion. Stir and filter the mixture to obtain sol A.

[0010] (4) Dissolve a certain amount of inorganic salt in the mixed solution of alcohol and water, and stir well to obtain sol B.

[0011] (5) Add the sol A obtained in step (3) to the sol B obtained in step (4) in proportion, and add propylene oxide. Stir well and then let it stand to obtain the silicon-based wet gel.

[0012] (6) Perform solvent replacement on the silicon-based wet gel obtained in step (5), and then age it at 20 - 120 °C for 24 - 72 h.

[0013] (7) Immerse the completely replaced wet gel in the mixed solution of alcohol, alkane compounds and modifiers for surface modification, and then immerse the modified wet gel in alkane compounds for solvent replacement 2 - 10 times, with an interval of 3 - 24 h each time. Finally, perform atmospheric drying to obtain the SiO 2 -based composite oxide aerogel.

[0014] Preferably, the solid waste raw materials described in step (1) are one or a mixture of fly ash, coal gangue, coal slime filter cake or steel slag.

[0015] Preferably, the alkaline solid powder described in step (2) is one or a mixture of sodium carbonate, sodium hydroxide or sodium bicarbonate; the mass ratio of the pre-treated powder to the alkaline solid powder is 1:(0.2 - 1); the calcination temperature is 400 - 1200 °C; the heating rate is 1 - 15 °C / min; the holding time is 1 - 8 h.

[0016] Preferably, the dilute acid solution described in step (3) is one or a mixture of nitric acid, sulfuric acid, hydrochloric acid, oxalic acid or acetic acid; the dilute acid concentration is 0.5 - 5 mol / L; the mass ratio of the activated powder to the dilute acid solution is 1:(5 - 15).

[0017] Preferably, the inorganic salt described in step (4) is AlCl3·6H 2 O, Al(NO3)3·9H 2One or several mixtures of O, Zr(NO3)4, ZrCl4, CeCl3 or Ce(NO3)3; the alcohol is one of methanol, ethanol, tert-butanol, isopropanol or n-decanol or a mixture thereof; the molar ratio of the inorganic salt, alcohol and water is 1:(5 - 30):(10 - 100).

[0018] Preferably, the mass ratio of sol A to sol B in step (5) is 1:(1 - 20); the molar ratio of the inorganic salt to propylene oxide is 1:(2 - 20).

[0019] Preferably, the solvent in step (6) is one of ethanol, methanol, acetone, ether, n-pentanol or isopropanol or a mixture thereof.

[0020] Preferably, the number of times of solvent replacement in step (6) is 3 - 15 times, and the interval time for each time is 3 - 24 h.

[0021] Preferably, the alkane compound in step (7) is one of n-hexane, n-heptane, cyclohexane or n-pentane or a mixture thereof; the modifier is one of trimethylchlorosilane, hexamethyldisilazane, methyltriethoxysilane, trimethylethoxysilane or phenyltriethoxysilane or a mixture thereof; the volume ratio of the alkane compound, modifier and alcohol is 1:(0.1 - 1):(0.1 - 1); the atmospheric pressure drying process adopts a gradient heating method, that is, the wet gel after surface modification is dried at 20 - 60 °C, 60 - 90 °C, 90 - 120 °C for 1 - 5 h respectively.

[0022] Beneficial effects:

[0023] (1) The method of the present invention uses bulk solid waste as the silicon source and another oxide component provided by the composite inorganic salt to prepare SiO 2 composite oxide aerogel, effectively realizing the molecular-level mixing between different raw materials, reducing the raw material cost, and largely solving the environmental pollution problem caused by bulk solid waste;

[0024] (2) By adopting the atmospheric pressure drying technology, the supercritical drying equipment that is essential for the production of aerogel in the traditional sense is abandoned, reducing the production cost, and the operation is safe and simple;

[0025] (3) The SiO 2 composite oxide aerogel prepared by this method has the characteristics of high porosity, large specific surface area and low thermal conductivity, and at the same time has ultra-high hydrophobic performance and heat insulation and flame retardant performance, which has positive significance for realizing the application of aerogel materials in the fields of architecture, energy conservation, chemical industry, aviation, etc. Description of the drawings:

[0026] Figure 1 For Al prepared in Example 1 2 O 3-SiO 2 Image of composite aerogel.

[0027] Figure 2 The Al prepared in Example 2 2 O 3 -SiO 2 Image of the hydrophobic angle of the composite aerogel. Specific implementation method:

[0028] The present invention is further described below with reference to examples, but the protection scope is not limited thereto.

[0029] Example 1

[0030] The fly ash was crushed and ground and sieved to 100 mesh, then mixed with sodium hydroxide in a mass ratio of 1:0.5, placed in a muffle furnace, calcined at 400°C and kept warm for 8 hours to obtain an activated powder, with a heating rate of 15°C / min. Then it was added to 2 mol / L dilute sulfuric acid for reaction, wherein the mass ratio of the activated powder to the dilute sulfuric acid was 1:5, and the clear liquid obtained after filtration was sol A. AlCl3·6H2O:methanol:water were fully mixed and stirred in a molar ratio of 1:5:10 to obtain sol B. Then, sol A and sol B were evenly mixed in a mass ratio of 1:1, and propylene oxide was added to the mixed solution, wherein the molar ratio of AlCl3·6H2O to propylene oxide was 1:2, and the mixed solution was allowed to stand after sufficient stirring to obtain a silicon-based wet gel. The silicon-based wet gel was immersed in methanol for solvent replacement three times, each time with an interval of 24 hours, and then aged at 90°C for 24 hours. Subsequently, the aged wet gel was immersed in a mixed solution of n-heptane: trimethylsilyl chloride: methanol with a volume ratio of 1:0.5:0.1 for hydrophobic modification. The modified wet gel was immersed in n-heptane for solvent replacement twice, each time with an interval of 24 hours. Finally, the modified wet gel was dried at 20°C for 1 hour, 60°C for 2 hours, and 90°C for 5 hours to obtain SiO2 composite oxide aerogel. Figure 1 As shown in the picture of the prepared Al2O3-SiO2 composite aerogel, the surface of the sample is uniformly white and the sample is very light. After characterization, it was found that the thermal conductivity of the SiO2 composite oxide aerogel material is 0.023W / (m·K), the BET specific surface area is 672.6m2 / g, the contact angle is 127°, and the density is 0.489g / cm3.

[0031] Example 2

[0032] The steel slag is crushed, ground and sieved to 400 mesh, and then uniformly mixed with sodium carbonate in a mass ratio of 1:0.2, put into a muffle furnace, calcined at 800 °C and kept warm for 3 h to obtain activated powder, with a heating rate of 6 °C / min. Then it is added to 5 mol / L dilute nitric acid for reaction, where the mass ratio of the activated powder to the dilute nitric acid is 1:10, and the clear liquid obtained after filtration is sol A. Al(NO3)3·9H2O: tert-butanol: water are fully mixed and stirred in a molar ratio of 1:30:60 to obtain sol B. Then, sol A and sol B are mixed evenly in a mass ratio of 1:7, and propylene oxide is added to the mixed solution, where the molar ratio of Al(NO3)3·9H2O to propylene oxide is 1:20. After sufficient stirring, it is left standing to obtain a silicon-based wet gel. The silicon-based wet gel is immersed in acetone for solvent replacement 15 times, with an interval of 3 h each time, then aged at 20 °C for 72 h, and subsequently the aged wet gel is immersed in a mixed solution of n-hexane: methyltrimethoxysilane: tert-butanol with a volume ratio of 1:0.1:0.5 for hydrophobic modification. The modified wet gel is immersed in n-hexane for solvent replacement 10 times, with an interval of 3 h each time. Finally, the modified wet gel is dried at 30 °C for 5 h, 70 °C for 3 h, and 120 °C for 1 h to obtain SiO2 composite oxide aerogel. The thermal conductivity of the prepared SiO2 composite oxide aerogel is 0.025 W / (m·K), and the hydrophobic angle is 139° (as Figure 2 shown). After characterization, it is found that the BET specific surface area of the SiO2 composite oxide aerogel material is 725.6 m2 / g, and the density is 0.474 g / cm3.

[0033] Example 3

[0034] The coal gangue was crushed and ground and sieved to 800 mesh, then mixed with sodium carbonate in a mass ratio of 1:1, placed in a muffle furnace, calcined at 1200°C and kept warm for 1h to obtain an activated powder, with a heating rate of 1°C / min. Then it was added to 0.5mol / L dilute hydrochloric acid for reaction, wherein the mass ratio of the activated powder to the dilute hydrochloric acid was 1:15, and the clear liquid obtained after filtration was sol A. ZrCl4: n-decyl alcohol: water were fully mixed and stirred in a molar ratio of 1:30:100 to obtain sol B. Then, sol A and sol B were evenly mixed in a mass ratio of 1:20, and propylene oxide was added to the mixed solution, wherein the molar ratio of ZrCl4 to propylene oxide was 1:8, and the mixed solution was allowed to stand after sufficient stirring to obtain a silicon-based wet gel. The silicon-based wet gel was immersed in ether for solvent replacement 3 times, each time with an interval of 24 hours, and then aged at 120℃ for 36 hours. The aged wet gel was then immersed in a mixed solution of n-hexane: trimethylethoxysilane: n-decyl alcohol with a volume ratio of 1:0.4:0.6 for hydrophobic modification. The modified wet gel was immersed in n-hexane for solvent replacement 4 times, each time with an interval of 12 hours. Finally, the modified wet gel was dried at 60℃ for 3 hours, 90℃ for 5 hours, and 100℃ for 5 hours to obtain SiO2 composite oxide aerogel. After characterization, it was found that the thermal conductivity of the SiO2 composite oxide aerogel material was 0.029W / (m·K), the BET specific surface area was 724.3m2 / g, the contact angle was 137°, and the density was 0.485g / cm3.

[0035] Example 4

[0036] The coal gangue was crushed, ground and sieved to 600 mesh, then mixed with sodium bicarbonate at a mass ratio of 1:0.7, placed in a muffle furnace, calcined at 900°C and kept warm for 5 hours to obtain an activated powder, with a heating rate of 4°C / min. Then it was added to 3 mol / L dilute oxalic acid for reaction, wherein the mass ratio of the activated powder to the dilute oxalic acid was 1:10, and the clear liquid obtained after filtration was sol A. CeCl3: ethanol: water was fully mixed and stirred at a molar ratio of 1:25:35 to obtain sol B. Then, sol A and sol B were evenly mixed at a mass ratio of 1:15, and propylene oxide was added to the mixed solution, wherein the molar ratio of CeCl3 to propylene oxide was 1:12, and the mixed solution was allowed to stand after sufficient stirring to obtain a silicon-based wet gel. The silicon-based wet gel was immersed in n-pentanol for solvent replacement 12 times, each time with an interval of 6 hours, and then aged at 90°C for 42 hours. The aged wet gel was then immersed in a mixed solution of cyclohexane: phenyltriethoxysilane: ethanol with a volume ratio of 1:0.6:0.3 for hydrophobic modification. The modified wet gel was immersed in cyclohexane for solvent replacement 6 times, each time with an interval of 9 hours. Finally, the modified wet gel was dried at 50°C for 5 hours, 80°C for 3 hours, and 120°C for 1 hour to obtain SiO2 composite oxide aerogel. After characterization, it was found that the thermal conductivity of the SiO2 composite oxide aerogel material was 0.027W / (m·K), the BET specific surface area was 784.6m2 / g, the contact angle was 142°, and the density was 0.466g / cm3.

[0037] Example 5

[0038] The coal slime filter cake was crushed and ground and sieved to 800 mesh, then mixed with sodium hydroxide in a mass ratio of 1:0.4, placed in a muffle furnace, calcined at 600°C and kept warm for 8h to obtain an activated powder, with a heating rate of 10°C / min. Then it was added to 4 mol / L dilute acetic acid for reaction, wherein the mass ratio of the activated powder to the dilute acetic acid was 1:5, and the clear liquid obtained after filtration was sol A. Ce(NO3)3: isopropanol: water was fully mixed and stirred in a molar ratio of 1:15:20 to obtain sol B. Then, sol A and sol B were evenly mixed in a mass ratio of 1:10, and propylene oxide was added to the mixed solution, wherein the molar ratio of Ce(NO3)3 to propylene oxide was 1:15, and the mixed solution was allowed to stand after sufficient stirring to obtain a silicon-based wet gel. The silicon-based wet gel was immersed in ethanol for solvent replacement 9 times, each time with an interval of 4 hours, and then aged at 50°C for 56 hours. Subsequently, the aged wet gel was immersed in a mixed solution of n-pentane: trimethylchlorosilane: isopropanol with a volume ratio of 1:0.8:0.4 for hydrophobic modification. The modified wet gel was immersed in n-pentane for solvent replacement 9 times, each time with an interval of 6 hours. Finally, the modified wet gel was dried at 60°C for 4 hours, 90°C for 3 hours, and 110°C for 2 hours to obtain SiO2 composite oxide aerogel. After characterization, it was found that the thermal conductivity of the SiO2 composite oxide aerogel material was 0.024W / (m·K), the BET specific surface area was 776.5m2 / g, the contact angle was 139°, and the density was 0.445g / cm3.

Claims

1. A method for preparing solid waste silicon-based composite oxide aerogel, the specific steps of which are as follows: (1) crushing and grinding the solid waste raw materials and sieving them to 100-800 meshes to obtain pre-treated powder; (2) uniformly mixing the pre-treated powder and the alkaline solid powder and placing them in a muffle furnace for high-temperature calcination to obtain an activated powder; (3) Grinding the activated powder and adding it into a dilute acid solution in proportion, stirring and filtering the mixed solution to obtain sol A; (4) dissolving a certain amount of inorganic salt in a mixture of alcohol and water and stirring thoroughly to obtain sol B; (5) adding the sol A obtained in step (3) to the sol B obtained in step (4) in proportion, adding propylene oxide, stirring thoroughly and then standing to obtain a silicon-based wet gel; (6) subjecting the silicon-based wet gel obtained in step (5) to solvent replacement, and then aging at 20 to 120° C. for 24 to 72 h; (7) The completely replaced wet gel is immersed in a mixed solution of alcohol, alkane compound and modifier for surface modification, and then the modified wet gel is immersed in an alkane compound for solvent replacement 2 to 10 times, each time at an interval of 3 to 24 hours, and finally dried at normal pressure to obtain SiO2-based composite oxide aerogel.

2. The method according to claim 1, characterized in that The solid waste raw material described in step (1) is one or a mixture of fly ash, coal gangue, coal slime filter cake or steel slag.

3. The method according to claim 1, characterized in that The alkaline solid powder described in step (2) is one of sodium carbonate, sodium hydroxide or sodium bicarbonate or a mixture thereof; the mass ratio of the pre-treated powder to the alkaline solid powder is 1:(0.2-1); the calcination temperature is 400-1200° C.; the heating rate is 1-15° C. / min; and the insulation time is 1-8 h.

4. The method according to claim 1, characterized in that The dilute acid solution described in step (3) is one or a mixture of nitric acid, sulfuric acid, hydrochloric acid, oxalic acid or acetic acid; the concentration of the dilute acid is 0.5-5 mol / L; the mass ratio of the activated powder to the dilute acid solution is 1:(5-15).

5. The method according to claim 1, characterized in that The inorganic salt described in step (4) is one or a mixture of AlCl3·6H2O, Al(NO3)3·9H2O, Zr(NO3)4, ZrCl4, CeCl3 or Ce(NO3)3; the alcohol is one or a mixture of methanol, ethanol, tert-butyl alcohol, isopropanol or n-decyl alcohol; the molar ratio of the inorganic salt, alcohol and water is 1:(5-30):(10-100).

6. The method according to claim 1, characterized in that In step (5), the mass ratio of sol A to sol B is 1:(1-20); the molar ratio of inorganic salt to propylene oxide is 1:(2-20).

7. The method according to claim 1, characterized in that The solvent in step (6) is one of ethanol, methanol, acetone, ether, n-pentanol or isopropanol, or a mixture thereof.

8. The method according to claim 1, characterized in that The number of solvent replacements in step (6) is 3 to 15 times, with an interval of 3 to 24 hours between each replacement.

9. The method according to claim 1, characterized in that The alkane compound described in step (7) is one of n-hexane, n-heptane, cyclohexane or n-pentane or a mixture thereof; the modifier is one of trimethylchlorosilane, hexamethyldisilazane, methyltriethoxysilane, trimethylethoxysilane or phenyltriethoxysilane or a mixture thereof; the volume ratio of the alkane compound, the modifier and the alcohol is 1:(0.1-1):(0.1-1); the atmospheric pressure drying process adopts a gradient temperature increase method, that is, the surface modified wet gel is dried at 20-60° C., 60-90° C. and 90-120° C. for 1-5 hours respectively.

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