Preparation method of ultra-low-density hydrophobic silicon dioxide aerogel powder

Abstract

The invention provides a preparation method of ultralow-density hydrophobic silicon dioxide aerogel powder. The preparation method comprises the following steps: S1, crushing silicon dioxide gel until the particle size D50 is not greater than 50 microns and the particle size D90 is not greater than 100 microns, and adding a solvent for replacement; and S2, mixing the gel replaced in the step S1 with hexamethyldisilazane and isooctane, heating in a water bath at 50-70 DEG C, modifying for 20-24 hours, drying under normal pressure after modification is finished, and crushing until the particle size D50 is not greater than 20 microns and the particle size D90 is not greater than 30 microns. According to the preparation method provided by the invention, the density of the obtained hydrophobic silicon dioxide aerogel powder is successfully controlled within an extremely low range, and the preparation method is stable in process, low in cost, high in efficiency, good in stability, free of agglomerated particles, good in fluidity and suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of silica aerogels, and more specifically, to a method for preparing ultra-low density hydrophobic silica aerogel powder. Background Art

[0002] Ultra-low density hydrophobic silica aerogel powder is a nano solid material with ultra-low density, low thermal conductivity, high porosity, light weight and high specific surface area. Due to its unique properties, silica aerogel powder has broad application prospects in building thermal insulation, chemical industry, environmental protection and other fields.

[0003] At present, there are mainly supercritical drying and atmospheric pressure drying for aerogel powder. Among them, supercritical drying has high cost, high requirements for equipment, large energy consumption and high industrial cost. Atmospheric pressure drying has low cost, simple process flow, and can be used for large-scale production. The modification process after atmospheric pressure drying is an important process for downstream applications of aerogel. At the same time, the traditional method for preparing silica aerogel powder has certain limitations, such as high production cost, long preparation cycle, poor mechanical properties, etc., which limit its promotion in practical applications. CN108047446A provides a method for preparing ultra-low density polyimide aerogel, which adopts sol-gel combined with organic-inorganic hybrid method, uniformly mixes ordinary silica aerogel particles with polyamic acid solution, forms composite gel through chemical imide process, and uses hydrofluoric acid to corrode silica aerogel to obtain pure polyimide gel, and uses supercritical drying process for drying to prepare polyimide aerogel material, which has complicated process and high cost. The supercritical process has high requirements for equipment and high energy consumption. Summary of the invention

[0004] The first object of the present invention is to provide a method for preparing ultra-low density hydrophobic silica aerogel powder. The preparation method is simple, has low production cost, and the obtained silica aerogel powder has low density.

[0005] The method for preparing the hydrophobic silica aerogel powder provided by the present invention comprises the following steps:

[0006] S1, crushing the silica gel to a particle size D50 of no more than 50 um and D90 of no more than 100 um, and adding a solvent for replacement;

[0007] S2, mixing the gel replaced in step S1 with hexamethyldisilazane and isooctane, and modifying the mixture in a water bath at 50-70°C for 20-24 hours. After the modification, drying the mixture under normal pressure to obtain a powder, and crushing the powder to a particle size D50 of not more than 20 um and D90 of not more than 30 um.

[0008] The applicant of the present invention has found that in the preparation process, before the silica gel is replaced, it is crushed to a particle size D50 (value) of no more than 50um and D90 (value) of no more than 100um, and the replaced gel is modified with hexamethyldisilazane, and then crushed to a particle size D50 (value) of no more than 20um and D90 (value) of no more than 30um after drying at normal pressure, and the density of the obtained silica aerogel powder is significantly reduced. At the same time, the preparation method does not require complicated exchange and drying steps, has low cost, and is suitable for industrial large-scale production.

[0009] In a specific embodiment of the present invention, in step S1, the silica gel can be prepared using a silica gel prepared by a commonly used preparation method in the art, such as using a sol-gel method to prepare the silica gel. In a preferred embodiment of the present invention, the preparation method of the silica gel comprises the following steps:

[0010] Tetraethoxysilane, alcohol and water are mixed, hydrochloric acid is added, and hydrolysis is carried out at 50-55°C. After the hydrolysis is completed, the pH value of the system is adjusted to 7-7.5. After the gel is completed, ethanol is added for aging.

[0011] In a preferred embodiment of the present invention, the alcohol may be ethanol. In a preferred embodiment of the present invention, the molar ratio of tetraethoxysilane, alcohol and water is 1:(8-10):(2.5-4). If the ratio is too low, the density of the sample obtained by the preparation method of the present invention may be too large and easy to collapse; if the ratio is too high, the thermal conductivity of the sample obtained by the preparation method of the present invention is too high.

[0012] In a specific embodiment of the present invention, the amount of hydrochloric acid added can be determined according to the amount of the silicon source substance. In a specific embodiment of the present invention, the amount of hydrochloric acid added can be 1 to 3 mL.

[0013] In a specific embodiment of the present invention, the hydrolysis time is generally 8 to 9 hours. After the hydrolysis is completed, a sol is obtained, and the pH value of the sol (the system after the hydrolysis is completed) can be adjusted to 7 to 7.5 using ammonia water and wait for gelation. After the gel is completed, ethanol can be used to age it. The specific steps of aging may include: adding ethanol to the gel at a water bath temperature of 60 to 70°C and aging for 20 to 24 hours. The amount of ethanol is controlled by those skilled in the art according to conventional methods of aging. After the aging is completed, the ethanol is removed to obtain silica gel.

[0014] In a preferred embodiment of the present invention, in order to further reduce the density of the obtained powder, in step S1, before replacing the silica gel, it is crushed to a particle size D50 (value) not greater than 35um and D90 (value) not greater than 80um, and it is further preferred to crush the silica gel to a particle size D50 (value) not greater than 28um and D90 (value) not greater than 55um. In a specific embodiment of the present invention, the crushing method commonly used in the art can be used for crushing. The present invention does not limit the crushing method, and it only needs to crush the particle size value to the desired size.

[0015] In a preferred embodiment of the present invention, in step S1, the solvent for replacement can be isooctane, n-hexane, etc. In the present invention, the replacement step is a conventional step in the art. Specifically, in the embodiment of the present invention, the replacement step can include: adding isooctane to the silica gel crushed to a particle size D50 of 5 to 10 um for replacement, the water bath temperature during replacement is 60 to 70°C, and the replacement time can be 20 to 30 hours. After the replacement is completed, the replacement solvent is removed to obtain the replaced gel for the next step.

[0016] In a preferred embodiment of the present invention, in step S2, the molar ratio of the hexamethyldisilazane to the silicon in the silica gel in step S1 is (1.2-1.4):1.

[0017] In a preferred embodiment of the present invention, in order to further reduce the density of the obtained powder, in step S2, the volume ratio of hexamethyldisilazane to isooctane is (0.1-0.5):1.

[0018] In a specific embodiment of the present invention, normal pressure drying is normal pressure drying commonly used in the art, such as normal pressure gradient drying, etc. In a preferred embodiment of the present invention, in step S2, the powder is crushed again to the desired particle size after normal pressure drying, and crushing the product to the desired particle size after normal pressure drying is also one of the core inventions of the present invention. In a preferred embodiment of the present invention, in order to further reduce the density of the obtained powder, in step S2, the powder obtained after drying under normal pressure is crushed to a particle size D50 (value) not greater than 10um and D90 (value) not greater than 23um.

[0019] Another object of the present invention is the ultra-low density hydrophobic silica aerogel powder obtained by the above preparation method.

[0020] The present invention adds a secondary specific crushing process in the specific preparation stage of the silica aerogel, and successfully controls the density of the obtained hydrophobic silica aerogel powder to an extremely low range (not higher than 0.03g / cm 3 , preferably not higher than 0.025 g / cm 3, further preferably not higher than 0.020 g / cm 3 ), and the preparation method provided by the present invention does not require ion exchange, nor does it require a complicated drying process. At the same time, the process is stable, the cost is low, the efficiency is high, and it can be applied to large-scale industrial production. The powder obtained by the preparation method has good stability, uniform particle size, no agglomerated particles, good fluidity, and good nanostructure and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the SEM image of the hydrophobic silica aerogel powder obtained in Example 1.

[0022] Figure 2 This is the pore size distribution diagram of the hydrophobic silica aerogel powder obtained in Example 1. DETAILED DESCRIPTION

[0023] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0024] Example 1

[0025] 1) Mix 0.1 mol of tetraethoxysilane, 1 mol of ethanol and 0.3 mol of water, stir, add 1 mL of 1 mol / l dilute hydrochloric acid, and stir at 50°C for 8 h.

[0026] 2) After the hydrolysis of the sol in step 1) is completed, the mixture is stirred at room temperature and ammonia water is added dropwise to control the pH of the sol at 7-7.5 and wait for gelation.

[0027] 3) Add 500 mL of ethanol to the gel obtained in step 2) to ensure that the gel is completely covered, and age in a 60° C. water bath for 24 h. After the aging is complete, remove the ethanol.

[0028] 4) The aged gel obtained in step 3) is crushed using a crusher to a particle size of D50 = 25.23 um and D90 = 50.46 um. At this time, there are no large particles in the sample. 500 mL of isooctane is added (ensuring that the crushed powder is completely submerged), and the mixture is replaced in a 60°C water bath for 24 hours. After the reaction is completed, the isooctane is removed to obtain a replaced gel.

[0029] 5) Add a modifier to the replaced gel obtained in step 4) (the modifier is prepared by using hexamethyldisilazane and isooctane in a volume ratio of 0.1 / 1, and the amount of the modifier is based on the molar ratio of hexamethyldisilazane to tetraethoxysilane being 1.4:1), and stir the modified gel in a 60°C water bath for 24 hours.

[0030] 6) After the reaction system of step 5) was placed in an oven for gradient drying (specific steps: drying at 90°C under normal pressure for 1h, drying at 110°C under normal pressure for 2h, and drying at 130°C under normal pressure for 2h), it was crushed again with a crushing grinder to a particle size of D50 = 9.85um, D90 = 20.21um, at which time there were no cohesive particles (with a certain fluidity and a fine powder feel), and a hydrophobic silica aerogel powder was obtained. The SEM image of the obtained powder is as follows Figure 1 As shown, from Figure 1 It can be seen that the aerogel presents a rich porous network structure, and the particle size is uniform, there is no agglomeration phenomenon, and the void distribution is uniform and stable, the pores are large, and the sample performance is good. Figure 2 The pore size distribution diagram of the obtained powder was obtained using a BET automatic adsorption instrument. From the diagram, it can be seen that the pore size of the aerogel powder is large and evenly distributed, which indicates that the aerogel has good nanostructure and mechanical properties.

[0031] Example 2

[0032] The method provided in this embodiment is the same as the method in Embodiment 1, except that:

[0033] In step (4), the aged gel obtained in step 3) is crushed using a crusher to a particle size of D50 = 30.25 um and D90 = 70.21 um;

[0034] In step (6), the powder is crushed again using a crushing grinder to a particle size of D50 = 15.87 um and D90 = 26.31 um.

[0035] Comparative Example 1

[0036] 1) Mix 0.1 mol of tetraethoxysilane, 1 mol of ethanol and 0.3 mol of water, stir, add 1 mL of 1 mol / l dilute hydrochloric acid, and stir at 50°C for 8 h.

[0037] 2) After the hydrolysis of the sol in step 1) is completed, the mixture is stirred at room temperature and ammonia water is added dropwise to control the pH of the sol at 7-7.5 and wait for gelation.

[0038] 3) Add 500 mL of ethanol to the gel obtained in step 2) to ensure that the gel is completely covered, and age in a 60° C. water bath for 24 h. After the aging is complete, remove the ethanol.

[0039] 4) Add 500 mL of isooctane (make sure that the aged gel is completely covered), and replace in a 60° C. water bath for 24 h. After the reaction is completed, remove the isooctane to obtain a replaced gel.

[0040] 5) Add a modifier to the replaced gel obtained in step 4) (the modifier is prepared by using hexamethyldisilazane and isooctane in a volume ratio of 0.1 / 1, and the amount of the modifier is based on the molar ratio of hexamethyldisilazane to tetraethoxysilane being 1.4:1), and stir the modified gel in a 60°C water bath for 24 hours.

[0041] 6) The reaction system of step 5) was placed in an oven for gradient drying (specific steps: drying at 90° C. and atmospheric pressure for 1 h, drying at 110° C. and atmospheric pressure for 2 h, and drying at 130° C. and atmospheric pressure for 2 h) to obtain hydrophobic silica aerogel powder.

[0042] Comparative Example 2

[0043] 1) Mix 0.1 mol of tetraethoxysilane, 1 mol of ethanol and 0.3 mol of water, stir, add 1 mL of 1 mol / l dilute hydrochloric acid, and stir at 50°C for 8 h.

[0044] 2) After the hydrolysis of the sol in step 1) is completed, the mixture is stirred at room temperature and ammonia water is added dropwise to control the pH of the sol at 7-7.5 and wait for gelation.

[0045] 3) Add 500 mL of ethanol to the gel obtained in step 2) to ensure that the crushed powder is completely covered, and age in a 60° C. water bath for 24 h. After aging, remove the ethanol.

[0046] 4) The aged gel obtained in step 3) is crushed using a crusher to a particle size of D50 = 25.23 um and D90 = 50.46 um. At this time, there are no large particles in the sample. 500 mL of isooctane is added (ensuring that the crushed powder is completely submerged), and the mixture is replaced in a 60°C water bath for 24 hours. After the reaction is completed, the isooctane is removed to obtain a replaced gel.

[0047] 5) Add a modifier to the replaced gel obtained in step 4) (the modifier is prepared by using hexamethyldisilazane and isooctane in a volume ratio of 0.1 / 1, and the amount of the modifier is based on the molar ratio of hexamethyldisilazane to tetraethoxysilane being 1.4:1), and stir the modified gel in a 60°C water bath for 24 hours.

[0048] 6) The reaction system of step 5) was placed in an oven for gradient drying (specific steps: drying at 90° C. and normal pressure for 1 h, drying at 110° C. and normal pressure for 2 h, and drying at 130° C. and normal pressure for 2 h) to obtain hydrophobic silica aerogel powder.

[0049] The properties of the hydrophobic silica aerogel powders obtained in the examples and comparative examples are shown in Table 1. Wherein, the density is the tap density, and the measurement method is based on GB / T 5211.4.

[0050] Table 1 Performance of hydrophobic silica aerogel powder

[0051] <![CDATA[Density / g / cm 3 > Example 1 0.020 Example 2 0.025 Comparative Example 1 0.045 Comparative Example 2 0.036

[0052] Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing ultra-low density hydrophobic silica aerogel powder, characterized in that: The steps include: S1, crushing the silica gel to a particle size D50 of no more than 50 um and D90 of no more than 100 um, and adding a solvent for replacement; S2, mixing the gel replaced in step S1 with hexamethyldisilazane and isooctane, and modifying it in a water bath at 50-70°C for 20-24h. After the modification, drying it under normal pressure and crushing it again to a particle size D50 of not more than 20um and D90 of not more than 30um.

2. The preparation method according to claim 1, characterized in that: In step S1, the method for preparing the silica gel comprises the following steps: Tetraethoxysilane, alcohol and water are mixed, hydrochloric acid is added, and hydrolysis is carried out at 50-55°C. After the hydrolysis is completed, the pH value of the system is adjusted to 7-7.5, and the gel is aged after completion.

3. The preparation method according to claim 2, characterized in that: The molar ratio of tetraethoxysilane, alcohol and water is 1:(8-10):(2.5-4).

4. The preparation method according to claim 2, characterized in that: The amount of hydrochloric acid added is 1 to 3 mL.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step S1, the solvent is isooctane.

6. The preparation method according to any one of claims 1 to 4, characterized in that: In step S1, the silica gel is crushed to a particle size D50 of no more than 35 um and D90 of no more than 80 um.

7. The preparation method according to any one of claims 1 to 4, characterized in that: In step S2, the molar ratio of the hexamethyldisilazane to the silicon in the silica gel is (1.2-1.4):

1.

8. The preparation method according to any one of claims 1 to 4, characterized in that: In step S2, the volume ratio of hexamethyldisilazane to isooctane is (0.1-0.5):

1.

9. The ultra-low density hydrophobic silica aerogel powder obtained by the preparation method according to any one of claims 1 to 8.

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