Method for preparing aerogel powder from waste gel

Abstract

The invention provides a method for preparing aerogel powder from waste gel, and belongs to the technical field of aerogel material preparation. The method comprises the following steps: by taking waste wet gel generated when an aerogel product is produced from an organic silicon source as a raw material, adding an ammonium fluoride solution, stirring and uniformly mixing, adding hexamethyldisiloxane, n-butyl alcohol and hydrochloric acid for modification, cooling and standing after modification, and separating out an upper-layer gel solution; stirring and cleaning with pure water, standing to obtain washing water, adding a sodium hydroxide aqueous solution, stirring and cleaning, and standing to obtain alkali washing water; and drying through closed-loop spray drying equipment to obtain the aerogel powder. According to the method, resource utilization of the waste gel is achieved, the production cost of the aerogel powder is reduced, environmental pollution is reduced, and the obtained aerogel powder has good hydrophobicity and heat insulation performance.

Description

Technical Field

[0001] This invention relates to the field of aerogel preparation, and more specifically to a method for preparing aerogel powder from waste gel. Background Technology

[0002] Aerogels are ultralight materials with nanoscale porous structures, possessing excellent properties such as low density, high specific surface area, and low thermal conductivity, and have broad application prospects in fields such as thermal insulation, adsorption separation, and catalyst supports. Currently, the main methods for preparing aerogel powders include the sol-gel method and the hydrothermal method, with the sol-gel method being the most commonly used. Traditional aerogel preparation processes typically include steps such as sol preparation, gelation, aging, solvent replacement, surface modification, and drying.

[0003] However, existing methods for preparing aerogel powders still have some problems: First, traditional aerogel powder production methods typically use high-purity silicon sources as raw materials, such as tetraethyl orthosilicate (TEOS) and tetramethoxysilane (TMOS). These raw materials are expensive, resulting in high production costs for aerogel products. Second, the production process of aerogel products often generates a large amount of waste gel, which typically contains ethanol, water, unreacted silicon source monomers, and incomplete gel networks. Although this approach has significant economic and environmental benefits, its practical reuse faces a series of severe technical challenges due to the inherent characteristics of the raw materials, limiting its efficient and high-value applications. First, the chemical composition and physical structure of waste gels are highly complex and heterogeneous. They contain both established three-dimensional networks and a large number of unreacted or partially reacted siloxane oligomers. More critically, the cross-linking degree of their gel networks is generally low and unevenly distributed, with numerous structural defects and uncondensed silanol groups (Si-OH). This inherent structural fragility makes it difficult for modifiers (such as hexamethyldisiloxane) to react uniformly and effectively with all active sites during direct hydrophobic modification, resulting in low direct modification efficiency. Insufficiently modified portions become weak points for structural collapse during the subsequent drying stage.

[0004] Secondly, existing recycling processes are insufficiently targeted, exacerbating the risk of structural damage. Conventional recycling approaches often simply redisperse the waste gel and then apply standard aerogel modification and drying processes. However, this process fails to address the fundamental weakness of uneven cross-linking in the waste gel. During subsequent atmospheric pressure drying, the gel skeleton needs to withstand enormous capillary forces. For waste gels with insufficient structural strength, this stress can easily cause irreversible collapse of their fragile nanoporous network, leading to the problem of easy collapse during drying. Ultimately, this results in inferior powder with a sharp decrease in specific surface area and an increase in density, whose performance is far inferior to products made from fresh raw materials.

[0005] Therefore, it is necessary to develop a method to specifically strengthen the incomplete gel network and achieve efficient and uniform hydrophobic modification based on this strengthening, thereby overcoming the bottleneck of structural collapse during the drying process. This is a key technical problem that needs to be solved in this field to realize the high-value and large-scale utilization of waste gels. In addition, existing aerogel powder preparation processes usually involve many steps and are complex, including sol preparation, gelation, aging, solvent replacement, surface modification and drying, which are not convenient for large-scale industrial production. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing aerogel powder from waste gel.

[0007] The technical solution of this invention: (1) Using the excess or waste wet gel from the production of aerogel products from organosilicon sources as raw materials, add ammonium fluoride solution, stir, grind and mix evenly, and add hexamethyldisiloxane, n-butanol and hydrochloric acid for modification; (2) After modification, cool and let stand, release the lower layer of modified waste liquid, and use pure water (i.e., water washing water) to stir and clean the upper layer of gel solution. Then, let stand and release the water washing water. Then, add sodium hydroxide aqueous solution (i.e., alkaline washing water) and stir to clean. After cleaning, let stand and release the alkaline washing water. Dry through a closed-circuit spray drying equipment to obtain aerogel powder.

[0008] According to the above scheme, in step (1), the gel is a wet gel that has not dried or hardened, containing ethanol, water, unreacted tetraethyl orthosilicate, wet gel with incomplete structural reaction, and wet gel with complete gelation; the concentration of ammonium fluoride solution is 0.1-5 mol / L, and the mass ratio of waste gel to ammonium fluoride solution is (50~200):(0.1-2); the concentration of hydrochloric acid is 25~35%.

[0009] According to the above scheme, in step (1), the mass ratio of waste gel to hexamethyldisiloxane, hydrochloric acid and n-butanol is (50~200): (150~300): (50~150): (1~20).

[0010] According to the above scheme, in step (1), the temperature for hydrophobic gel modification is 40~80℃; the stirring speed is 100~1000rpm / min; and the modification time is 1~12h.

[0011] According to the above scheme, in step (2), the concentration of sodium hydroxide aqueous solution is 0.01~0.05mol / L; the mass ratio of gel solution to washing water and alkaline washing water is (100~400):(100~300):(100~300); the washing time of pure water and sodium hydroxide aqueous solution is 0.1~1h; the rotation speed of pure water and sodium hydroxide aqueous solution during washing is 100~1000rpm / min; the standing time is 0.1~1h; the drying temperature of gel is 70~150℃; and the drying time is 1~12h.

[0012] According to the above scheme, in step (2), the inlet air temperature for drying the gel is 50~200℃, and the outlet air temperature for drying is 50~200℃.

[0013] The present invention has the following beneficial effects: 1. This invention uses excess or waste wet gel from organosilicon sources during the production of aerogel products as raw materials. By adding ammonium fluoride solution, the unreacted and incompletely gelled silicon sources are further reacted to generate a fully structured wet gel. Hexamethyldisiloxane and hydrochloric acid are added to modify it for hydrophobicity. After the gel is washed, it is dried using a closed-circuit spray drying device. The resulting silica aerogel powder has good hydrophobic properties and extremely low thermal conductivity.

[0014] 2. This invention does not simply redisperse waste gels; it also constructs a system (ammonium fluorosilicate / oxalic acid / β-cyclodextrin / N-β-aminoethyl-γ-aminopropyltrimethoxysilane) that can identify and repair fragile networks with low cross-linking and incomplete structures in waste gels, fundamentally strengthening their gel skeleton. This provides a structurally stable foundation for subsequent hydrophobic modification and drying, solving the two major problems of low efficiency in direct modification and easy collapse during drying in waste gel recycling. Ammonium fluorosilicate, as an integrated catalyst and network source, simultaneously provides F⁻, H⁺, and embeddable silicon species, exhibiting higher repair efficiency than simple corrosion. Oxalic acid, as a rate regulator, can finely adjust the catalytic reaction rate with its weak acidity, avoiding excessively rapid local gelation. β-cyclodextrin, through its cavity structure, encapsulates and slowly releases active species, greatly improving the uniformity of the network structure. N-β-aminoethyl-γ-aminopropyltrimethoxysilane (diaminosilane) provides twice the number of chemical anchoring sites with its diamino structure and can form a dynamic hydrogen bond network, significantly enhancing the mechanical strength and toughness of the repaired network.

[0015] 3. This invention utilizes the waste gel generated during the production of aerogel products as raw material, reducing raw material costs and simplifying the operation steps of the production process, effectively solving the problem of waste gel disposal. 4. The present invention has a simple process, low cost, is easy to operate, saves production costs, and saves manpower and material resources, making it particularly suitable for industrial production; 5. The aerogel powder prepared by this invention is a non-toxic, harmless, green and environmentally friendly product that meets modern environmental protection requirements. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Detection method: Particle size The particle size of the aerogel powder was obtained by adding it to a Venturi tube using laser diffraction / scattering and dry dispersion with compressed air.

[0018] Specific surface area Using the BET method, a small amount of aerogel powder (usually 50-200 mg) is accurately weighed and placed into a sample tube. The tube is then heat-treated at 200°C for 2 hours under vacuum. The sample tube is then connected to an instrument and immersed in liquid nitrogen for testing. The specific surface area of ​​the sample is obtained by the nitrogen desorption curve.

[0019] Shrinkage The surface area was compared with the pore volume shrinkage rate obtained by BET test.

[0020] thermal conductivity The transient planar heat source method is employed, in which electrodes are inserted into vibrated aerogel powder, and a constant instantaneous current is applied to the probe to generate a temperature rise. Simultaneously, the change in resistance (temperature) over time is recorded. By analyzing the temperature rise curve, the thermal conductivity and thermal diffusivity of the material can be calculated simultaneously.

[0021] Example 1 (without N-β-aminoethyl-γ-aminopropyltrimethoxysilane) Step 1: Take 100 parts of waste gel, add 1.2 parts of 0.5mol / L ammonium fluorosilicate solution, 0.2 parts of oxalic acid and 0.1 parts of β-cyclodextrin, put them into a high-speed shear stirring device, and grind them at 300rpm / min for 20min to form a uniform slurry gel. During the process, the temperature is controlled at 35℃ by water bath.

[0022] Step 2: Without any bridging reaction, the modifier and solvent were added sequentially according to the mass ratio of waste gel: hexamethyldisiloxane: hydrochloric acid: n-butanol = 100:220:110:12. The temperature was raised to 65°C, the stirring speed was increased to 600 rpm / min, and the modification was continued for 8 hours to complete the hydrophobic modification.

[0023] Step 3: After modification, cool to room temperature and let stand for 40 minutes to separate into layers. Discard the lower layer of waste liquid. Take 200 parts of the upper gel solution, add 200 parts of pure water, stir and wash at 500 rpm for 35 minutes, let stand for 35 minutes, and discard the wash water. Then add 200 parts of 0.03 mol / L sodium hydroxide aqueous solution, stir and wash at the same speed for 35 minutes, let stand for 35 minutes, and discard the alkaline wash water. Send the washed gel into a closed-circuit spray drying equipment, set the inlet air temperature to 160℃ and the outlet air temperature to 110℃, and dry for 6 hours to obtain aerogel powder.

[0024] The particle size is 10-50 μm, the specific surface area is 679.8 m² / g, the shrinkage rate is 24.1%, and the thermal conductivity is 0.0152 W / (m·K). Relatively uniform catalytic repair was achieved using an ammonium fluorosilicate / oxalic acid / cyclodextrin system. However, relying solely on physical repair and enhancement without strong chemical bridging still cannot solve the problem of waste gel fragmentation. Example 2 Step 1: Take 100 parts of waste gel, add 1.2 parts of 0.5mol / L ammonium fluorosilicate solution, 0.2 parts of oxalic acid and 0.1 parts of β-cyclodextrin, put it into a high-speed shear stirring device, and grind it at 300rpm / min for 20min. Then add 2 parts of a 95% ethanol mixture of N-β-aminoethyl-γ-aminopropyltrimethoxysilane (volume ratio 1:10) and stir. Continue grinding for 5min. N-β-aminoethyl-γ-aminopropyltrimethoxysilane is mixed with 95% ethanol solution at a volume ratio of 1:10 and then added to form a uniform slurry gel. During the process, the temperature is controlled at 35℃ by water bath. Step 2: Add the modifier and solvent sequentially according to the mass ratio of waste gel: hexamethyldisiloxane: hydrochloric acid: n-butanol = 100:220:110:12, heat to 65℃, increase the stirring speed to 600 rpm / min, and continue the modification for 8 hours to complete the hydrophobic modification.

[0025] Step 3: After modification, cool to room temperature and let stand for 40 minutes to separate into layers. Discard the lower layer of waste liquid. Take 200 parts of the upper gel solution, add 200 parts of pure water, stir and wash at 500 rpm for 35 minutes, let stand for 35 minutes, and discard the wash water. Then add 200 parts of 0.03 mol / L sodium hydroxide aqueous solution, stir and wash at the same speed for 35 minutes, let stand for 35 minutes, and discard the alkaline wash water. Send the washed gel into a closed-circuit spray drying equipment, set the inlet air temperature to 160℃ and the outlet air temperature to 110℃, and dry for 6 hours to obtain aerogel powder.

[0026] With a specific surface area of ​​784.6 m² / g, a thermal conductivity of 0.0141 W / (m·K), and a shrinkage rate of 14.3%, the composite catalytic system of this invention exhibits a perfect synergistic effect: ammonium fluorosilicate smoothly releases active species under the regulation of oxalic acid, β-cyclodextrin guides its preferential repair of network defects, and diaminosilane strongly bridges the activated fragments, forming a robust and unified network. This network can resist drying stress to a great extent, thereby preserving the nanoporous structure with high fidelity, ultimately achieving high-performance recycling of waste gels.

[0027] Example 3 Based on Example 2, in step one, ammonium fluorosilicate solution, oxalic acid, and β-cyclodextrin were added, and the mixture was stirred and ground at 300 rpm for 30 min. The rest was the same as in Example 3. The obtained powder had a specific surface area of ​​792.3 m² / g, a thermal conductivity of 0.0140 W / (m·K), and a shrinkage rate of 13.1%. Extending the catalytic repair time to 30 minutes slightly optimized the specific surface area and shrinkage rate of the powder. This demonstrates that providing sufficient reaction time facilitates a more thorough repair of deep network defects by the ammonium fluorosilicate / cyclodextrin composite catalyst, laying a more solid foundation for subsequent bridging and resulting in a more complete final network structure.

[0028] Example 4 Based on Example 2, 2.5 parts of N-β-aminoethyl-γ-aminopropyltrimethoxysilane were used. Other aspects were the same as in Example 3. The resulting powder has a specific surface area of ​​816.9 m² / g, a thermal conductivity of 0.0138 W / (m·K), and a shrinkage rate of 11.2%, indicating that the present invention has good parameter adjustability. For waste gels with poorer cross-linking or lower strength, more intense remediation can be achieved by enhancing the catalytic and bridging effects. Example 5 Based on Example 2, in step one, ammonium fluorosilicate solution, oxalic acid, and β-cyclodextrin were added, and the mixture was stirred and ground at 400 rpm for 15 min. The rest was the same as in Example 3. The resulting powder has a specific surface area of ​​779.2 m² / g, a thermal conductivity of 0.0142 W / (m·K), and a shrinkage rate of 13.4%, demonstrating the high reactivity and efficiency of the composite catalytic system of this invention. The synergistic effect among the components enables the repair-bridging process to be completed rapidly in a short time. Example 6 Step 1: Take 100 parts of waste gel, add 1 part of 0.5mol / L ammonium fluoride solution, put it into a high-speed shear stirring device, and grind it at 300rpm / min for 20min to form a uniform slurry gel, and control the temperature at 25℃.

[0029] Step 2: Add the modifier and solvent sequentially according to the mass ratio of waste gel: hexamethyldisiloxane: hydrochloric acid: n-butanol = 100:200:100:10, heat to 60℃, increase the stirring speed to 500 rpm / min, and continue the modification for 6 hours to complete the hydrophobic modification.

[0030] Step 3: After modification, cool to room temperature and let stand for 30 minutes to separate into layers. Discard the lower layer of waste liquid. Take 200 parts of the upper gel solution, add 200 parts of pure water, stir and wash at 500 rpm for 30 minutes, let stand for 30 minutes, and discard the wash water. Then add 200 parts of 0.03 mol / L sodium hydroxide aqueous solution, stir and wash at the same speed for 30 minutes, let stand for 30 minutes, and discard the alkaline wash water. Send the washed gel into a closed-loop spray drying equipment, set the inlet air temperature to 150℃ and the outlet air temperature to 100℃, and dry for 6 hours to obtain aerogel powder.

[0031] The resulting powder has a specific surface area of ​​only 427.6 m² / g, a particle size of 10-50 μm, a shrinkage rate as high as 36.8%, and a poor thermal conductivity of 0.0183 W / (m·K). This indicates that while simple catalysis using only ammonium fluoride can promote partial condensation, it may not be able to systematically repair the inherently uneven and fragile network framework of the waste gel. Its structural strength is insufficient to resist capillary forces during the drying process, leading to large-scale network collapse during the drying stage.

[0032] Comparative Example 1 Step 1: Take 100 parts of waste gel, add 1.2 parts of 0.5mol / L ammonium fluorosilicate solution, 0.2 parts of oxalic acid, 0.1 parts of β-cyclodextrin, and 1.85 parts of monoaminosilane (KH550). Place the mixture in a high-speed shear stirring device and grind it at 300rpm / min for 20min to form a uniform slurry gel. During the process, the temperature is controlled at 35℃ using a water bath.

[0033] Step 2: Add the modifier and solvent sequentially according to the mass ratio of waste gel: hexamethyldisiloxane: hydrochloric acid: n-butanol = 100:220:110:12, heat to 65℃, increase the stirring speed to 600 rpm / min, and continue the modification for 8 hours to complete the hydrophobic modification.

[0034] Step 3: After modification, cool to room temperature and let stand for 40 minutes to separate into layers. Discard the lower layer of waste liquid. Take 200 parts of the upper gel solution, add 200 parts of pure water, stir and wash at 500 rpm for 35 minutes, let stand for 35 minutes, and discard the wash water. Then add 200 parts of 0.03 mol / L sodium hydroxide aqueous solution, stir and wash at the same speed for 35 minutes, let stand for 35 minutes, and discard the alkaline wash water. Send the washed gel into a closed-circuit spray drying equipment, set the inlet air temperature to 160℃ and the outlet air temperature to 110℃, and dry for 6 hours to obtain aerogel powder.

[0035] The particle size is 10-50 μm, the specific surface area is 651.4 m² / g, the shrinkage rate is 26.9%, and the thermal conductivity is 0.0154 W / (m·K). Monoamino silanes (KH550) have limited bridging ability and network toughness due to their single chemical anchoring point. Unlike diamino silanes, they cannot form denser covalent crosslinks through double the anchoring points and utilize the dynamic hydrogen bond network constructed by the diamino groups to dissipate stress. Therefore, the repaired network exhibits higher shrinkage when coping with drying stress.

[0036] Comparative Example 2 Step 1: Take 100 parts of waste gel, add 1.2 parts of 0.5mol / L ammonium fluorosilicate solution, 0.1 parts of β-cyclodextrin and 2 parts of diaminosilane, put them into a high-speed shear stirring device, and grind them at 300rpm / min for 20min to form a uniform slurry gel. During the process, the temperature is controlled at 35℃ by water bath.

[0037] Step 2: Add the modifier and solvent sequentially according to the mass ratio of waste gel: hexamethyldisiloxane: hydrochloric acid: n-butanol = 100:220:110:12, heat to 65℃, increase the stirring speed to 600 rpm / min, and continue the modification for 8 hours to complete the hydrophobic modification.

[0038] Step 3: After modification, cool to room temperature and let stand for 40 minutes to separate into layers. Discard the lower layer of waste liquid. Take 200 parts of the upper gel solution, add 200 parts of pure water, stir and wash at 500 rpm for 35 minutes, let stand for 35 minutes, and discard the wash water. Then add 200 parts of 0.03 mol / L sodium hydroxide aqueous solution, stir and wash at the same speed for 35 minutes, let stand for 35 minutes, and discard the alkaline wash water. Send the washed gel into a closed-circuit spray drying equipment, set the inlet air temperature to 160℃ and the outlet air temperature to 110℃, and dry for 6 hours to obtain aerogel powder.

[0039] The resulting powder exhibits a particle size of 10-50 μm, a specific surface area of ​​566.2 m² / g, a shrinkage rate of 27.3%, and a thermal conductivity of 0.0168 W / (m·K), indicating that the shrinkage rate remains relatively high. This demonstrates that in the absence of oxalic acid as a rate modifier, the catalytic reaction rate of ammonium fluorosilicate is excessively rapid and difficult to control, easily leading to the formation of overly dense cross-linking points in localized areas of the gel, while other areas suffer insufficient repair. This results in stress concentration within the network, causing significant shrinkage during drying.

[0040] Comparative Example 3 Step 1: Take 100 parts of waste gel, add 1.2 parts of 0.5mol / L ammonium fluorosilicate solution, 0.2 parts of oxalic acid and 2 parts of diaminosilane, put them into a high-speed shear stirring device, and grind them at 300rpm / min for 20min to form a uniform slurry gel. During the process, the temperature is controlled at 35℃ by water bath.

[0041] Step 2: Add the modifier and solvent sequentially according to the mass ratio of waste gel: hexamethyldisiloxane: hydrochloric acid: n-butanol = 100:220:110:12, heat to 65℃, increase the stirring speed to 600 rpm / min, and continue the modification for 8 hours to complete the hydrophobic modification.

[0042] Step 3: After modification, cool to room temperature and let stand for 40 minutes to separate into layers. Discard the lower layer of waste liquid. Take 200 parts of the upper gel solution, add 200 parts of pure water, stir and wash at 500 rpm for 35 minutes, let stand for 35 minutes, and discard the wash water. Then add 200 parts of 0.03 mol / L sodium hydroxide aqueous solution, stir and wash at the same speed for 35 minutes, let stand for 35 minutes, and discard the alkaline wash water. Send the washed gel into a closed-circuit spray drying equipment, set the inlet air temperature to 160℃ and the outlet air temperature to 110℃, and dry for 6 hours to obtain aerogel powder.

[0043] The obtained powder, with a particle size of 10-50 μm, a specific surface area of ​​639.8 m² / g, a shrinkage rate of 22.9%, and a thermal conductivity of 0.0159 W / (m·K), is still unsatisfactory. This indicates that the absence of β-cyclodextrin prevents the effective transport of active fluorosilicate ions, which preferentially act on defects and weak points in the gel network, resulting in insufficient uniformity of the repaired network and thus affecting the overall structural stability and thermal insulation performance. The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing aerogel powder from waste gel, characterized in that, Includes the following steps: (1) Use the excess or waste wet gel from the production of aerogel products from organosilicon sources as raw materials, add ammonium fluoride solution, stir, grind and mix evenly; (2) Modification was carried out by adding hexamethyldisiloxane, n-butanol and hydrochloric acid; (3) After modification, cool and let stand, release the lower layer of modified waste liquid, and use pure water (i.e., water washing water) to stir and clean the upper layer of gel solution. Then let stand and release the water washing water. Then add sodium hydroxide aqueous solution (i.e., alkaline washing water) and stir to clean. After cleaning, let stand and release the alkaline washing water. Dry through a closed-circuit spray drying equipment to obtain aerogel powder.

2. The method for preparing aerogel powder from waste gel according to claim 1, characterized in that, In step (1), the waste gel is a wet gel that has not dried or hardened, and contains ethanol, water, unreacted tetraethyl orthosilicate, wet gel with incomplete structural reaction and wet gel with complete gelation; the concentration of ammonium fluoride solution is 0.1-5 mol / L, and the mass ratio of waste gel to ammonium fluoride solution is (50~200):(0.1-2).

3. The method for preparing aerogel powder from waste gel according to claim 2, characterized in that, In step (1), ammonium fluoride can also be a complex of ammonium fluorosilicate, wherein the mass ratio of ammonium fluorosilicate: oxalic acid: β-cyclodextrin: N-β-aminoethyl-γ-aminopropyltrimethoxysilane in the complex system is (8-15): (1.5-2.5): (0.01-0.3): (1-20); the grinding conditions are to grind the mixture into a slurry at a speed of 500-800 rpm and to continuously stir it at 30-40℃ for 20-30 min.

4. The method for preparing aerogel powder from waste gel according to claim 3, characterized in that, In step (1), after adding ammonium fluorosilicate, oxalic acid, and β-cyclodextrin and grinding and stirring, N-β-aminoethyl-γ-aminopropyltrimethoxysilane is added and stirred, and grinding is continued for 5-20 minutes. N-β-aminoethyl-γ-aminopropyltrimethoxysilane is mixed with 95% ethanol solution at a volume ratio of 1:10 and then added.

5. The method for preparing aerogel powder from waste gel according to claim 1, characterized in that, In step (2), the concentration of hydrochloric acid is 25-35%, and the mass ratio of waste gel to hexamethyldisiloxane, hydrochloric acid and n-butanol is (50-200): (150-300): (50-150): (1-20).

6. The method for preparing aerogel powder from waste gel according to claim 1, characterized in that, In step (2), the temperature for hydrophobic gel modification is 40~80℃; the stirring speed is 100~1000rpm / min; and the modification time is 1~12h.

7. The method for preparing aerogel powder from waste gel as described in claim 1, characterized in that, In step (2), the concentration of the sodium hydroxide aqueous solution is 0.01~0.05mol / L; the mass ratio of gel solution to water and alkaline water is (100~400):(100~300):(100~300); the washing time with pure water and sodium hydroxide aqueous solution is 0.1~1h, the washing speed is 100~1000rpm / min; the standing time is 0.1~1h; the drying temperature of the gel is 70~150℃; and the drying time is 1~12h.

8. The method for preparing aerogel powder from waste gel as described in claim 1, characterized in that, In step (2), the inlet air temperature for drying the gel is 50~200℃, and the outlet air temperature for drying is 50~200℃.