A superhydrophobic silica aerogel material and its preparation method

Abstract

The present invention relates to the technical field of aerogel material production, and particularly relates to a superhydrophobic silica aerogel material and a preparation method thereof. The method provided by the present invention is to prepare a superhydrophobic silica aerogel using a chlorosilane azeotrope. By controlling the reaction temperature, introducing water in multiple steps under the action of an alcohol solvent, the problems in the process of preparing silica aerogel using a chlorosilane azeotrope are solved, including the difficulty in forming a gel due to different hydrolysis rates of silicon tetrachloride and trimethylchlorosilane, the difficulty in hydrophobic modification, and the complex preparation process and high preparation cost caused by the need to add an external hydrophobic modifier during the preparation of the aerogel. Finally, the prepared superhydrophobic silica aerogel material has excellent heat insulation performance and superhydrophobic properties. Moreover, the preparation method provided by the present invention is simple and has a low preparation cost, which not only realizes the resource utilization of the chlorosilane azeotrope but also endows the chlorosilane azeotrope with high economic value.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel material production, and particularly to a superhydrophobic silica aerogel material and a preparation method thereof. Background Art

[0002] Silica (SiO2) aerogel is a porous material with excellent heat insulation, sound insulation, shock absorption, selective adsorption and other properties, and has broad application potential in the fields of mechanics, optics, acoustics, electrical and electronics, thermotics, aerospace, architecture, and adsorption separation. At present, the preparation of silica aerogel usually involves catalytic hydrolysis of a silicon source to obtain silica sol, and then the silica sol is prepared into aerogel through steps such as gelation, aging, and drying.

[0003] In recent years, the production capacity of the silicone industry has been continuously developed, the preparation processes of silicone alkane production enterprises have gradually matured, the production capacity has been continuously improved, and the amount of industrial by-products has also been continuously increasing. Methylchlorosilane is the main monomer for synthesizing silicone polymers, used for manufacturing silicone resins and rubbers, formulating silicone adhesives and sealants, and also for producing silane coupling agents, with a wide range of uses. However, during the production of methylchlorosilane, an industrial by-product - chlorosilane azeotrope will be generated. The main components of the chlorosilane azeotrope are trimethylchlorosilane and silicon tetrachloride, which can react with water to produce hydrogen chloride, so it has strong corrosiveness and strong pollution, and the treatment cost is relatively high. Recycling the chlorosilane azeotrope and turning waste into treasure is a better way to deal with the chlorosilane azeotrope.

[0004] Research shows that both trimethylchlorosilane and silicon tetrachloride in the chlorosilane azeotrope are silicon sources for producing silica aerogel. For example, Chinese Patent Application CN115010140A prepared superhydrophobic aerogel through hydrolysis, gelation, drying and other processes using components such as trimethylchlorosilane and alcohol; Chinese Patent Application CN101863480A prepared silica aerogel using raw materials such as silicon tetrachloride and water through hydrolysis, gelation, drying and other steps. Therefore, using the chlorosilane azeotrope to prepare silica aerogel may be a better way to realize the resource utilization of the chlorosilane azeotrope, with good prospects. However, due to the large difference in the hydrolysis rates of silicon tetrachloride and trimethylchlorosilane, directly reacting the chlorosilane azeotrope with alcohol will result in difficulty or inability to form a gel, and directly generate white powder or flocculent precipitate; and even if a gel can be formed, the finally prepared aerogel product cannot be well hydrophobized. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a silica aerogel material using a chlorosilane azeotrope by controlling the reaction temperature and introducing water in multiple steps, and obtains a superhydrophobic silica aerogel material. The specific technical solutions are as follows:

[0006] In the first aspect of the present invention, a method for preparing a superhydrophobic silica aerogel material is provided, comprising the following steps:

[0007] Step 1: Drop a chlorosilane azeotrope into an aqueous alcohol solution, react at 10 °C, continuously discharge the generated hydrogen chloride during the reaction, and then separate ethanol and hydrogen chloride after the reaction to obtain a reaction solution;

[0008] Step 2: Drop the aqueous alcohol solution into the reaction solution again, react at 10 °C, and continuously discharge the generated hydrogen chloride gas during the reaction to obtain a hydrophobic silica sol;

[0009] Step 3: Add an alcoholic alkali solution to the silica sol, stir evenly, then let it stand for gelation, and wash it after gelation to obtain a wet silica gel material;

[0010] Step 4: Dry to obtain a superhydrophobic silica aerogel material.

[0011] Preferably, in Steps 1 and 2, the aqueous alcohol solution is a mixed solution of alcohol and water, the alcohol is selected from one of ethanol, methanol, and ethylene glycol, and the water is pure water or deionized water;

[0012] Preferably, the temperature of the aqueous alcohol solution in Steps 1 and 2 is 0 - 10 °C. Controlling the aqueous alcohol solution at a lower temperature is to ensure that the reaction in Step 1 proceeds at a lower temperature, which can control the reaction rate and is more conducive to forming a sol and realizing the hydrophobicization of the sol;

[0013] Preferably, in Step 1, the content of trimethylchlorosilane in the chlorosilane azeotrope is 40 - 60 wt%, and the content of silicon tetrachloride is 30 - 55 wt%.

[0014] Preferably, the reaction time in Step 1 is 0.5 - 1 h.

[0015] Preferably, the separation of ethanol and hydrogen chloride in Step 1 is achieved by distillation and reflux. The temperature of the distillation is 50 - 70 °C, and the reflux time is 2 - 4 h.

[0016] Preferably, the molar ratio of alcohol to water in the aqueous alcohol solution in Step 1 is 10 - 13:0.4 - 0.8.

[0017] Preferably, the molar ratio of alcohol to water in the aqueous alcohol solution in Step 2 is 10 - 13:1 - 2, and the alcohol in the aqueous alcohol solution is the same as the alcohol used in the aqueous alcohol solution in Step 1; the alcohol is selected from methanol, ethanol, or ethylene glycol. The alcohol serves as a solvent on the one hand and realizes the alcoholysis of silicon tetrachloride of the raw materials on the other hand.

[0018] Preferably, the reaction time in Step 2 is 0.5 - 1 h.

[0019] Preferably, the mass ratio of the aqueous alcohol solution and the chlorosilane azeotrope added dropwise twice in the step 1 and the step 2 is 0.8-1.6:1; and the mass of water in the aqueous alcohol solution added in the step 1 is less than the mass of water in the aqueous alcohol solution added in the step 2.

[0020] The hydrolysis reaction of silicon tetrachloride is very violent in an environment with a large amount of water. The hydrogen chloride generated by the reaction dissolves in water to form an acidic environment, which is even more unfavorable for the hydrolysis of silicon tetrachloride. Under the amount of alcohol and alcohol added in this application, to a certain extent, it alleviates and protects the normal progress of the reaction. The degree of direct hydrolysis of silicon tetrachloride is small, and the proportion of tetraethyl orthosilicate generated by alcoholysis is large. Then it reacts with water to hydrolyze to form silica gel. Therefore, the water content in the second aqueous alcohol solution is greater than the water content in the first aqueous alcohol solution.

[0021] Preferably, the alcohol-alkali solution is a mixed solution of alcohol, alkali and water, and the molar ratio of alcohol, alkali and water is 2-4:3×10 -3 ~3×10 -2 :0.01-0.1, and the alcohol used in the alcohol-alkali solution is the same as the alcohol in the aqueous alcohol solution in the step 1; the alkali is selected from at least one of sodium hydroxide and ammonia water; in the step 3, the alcohol-alkali solution is added until the pH of the silica sol is 3.5-5.

[0022] Preferably, in the step 3, the washing is carried out using water.

[0023] Preferably, the time for standing the gel in the step 3 is 0.5-3 h.

[0024] In some aspects, in the step 3, after adding the alcohol-alkali solution to the silica sol and stirring evenly, fiber materials are added and fully impregnated, then left to stand for gelation. After gelation, solvent replacement is carried out to obtain a wet silica gel material.

[0025] Preferably, the solvent for solvent replacement is n-hexane, hexamethyldisiloxane or ethanol, and the process of solvent replacement is to soak in the above solvent for 24-48 h.

[0026] Preferably, the fiber material is short fiber or fiber felt. The short fiber is selected from at least one of short aramid fiber, short basalt fiber, short glass fiber and short carbon fiber, and the fiber felt is selected from one of basalt fiber felt, glass fiber felt, ceramic fiber felt and carbon fiber felt;

[0027] Preferably, the step 3 further includes a step of removing excess gel.

[0028] Preferably, the drying in the step 4 is atmospheric drying or supercritical drying; the atmospheric drying includes freeze drying and spray drying; the temperature of the spray drying is 120-140 °C, and the inlet air volume is 100%; the medium for the supercritical drying is carbon dioxide or ethanol.

[0029] In a second aspect of the present invention, there is provided a superhydrophobic silica aerogel material prepared by using the method described in any one of the above.

[0030] By controlling the temperature and introducing water in multiple steps during the reaction process, the present invention controls the hydrolysis rate of silicon tetrachloride and trimethylchlorosilane in the chlorosilane azeotrope, and while not affecting the construction process of the silicon tetrachloride gel framework, ensures uniform grafting on the surface of the formed silica sol after the hydrolysis of trimethylchlorosilane, enabling the simultaneous progress of the sol preparation and the hydrophobic modification process of the sol. The beneficial effects brought by the technical solution of the present invention are as follows:

[0031] (1) The method of the present invention uses a chlorosilane azeotrope as a raw material to prepare a superhydrophobic silica aerogel material, solving the problems in the preparation of existing hydrophobic silica aerogels, such as the need for adding external hydrophobic modifiers, complex preparation processes, and high preparation costs. It not only realizes the resource utilization of the chlorosilane azeotrope but also endows the methylchlorosilane azeotrope with high economic value.

[0032] (2) By controlling the reaction temperature and introducing water in multiple steps, the present invention solves the problems of difficult gelation and poor hydrophobic modification effect during the preparation of aerogels using chlorosilane azeotropes. Finally, the prepared superhydrophobic silica aerogel has excellent heat insulation performance and superhydrophobic properties. Specific Embodiments

[0033] The technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application.

[0034] Example 1

[0035] Step 1: 240 g of a chlorosilane azeotrope (mainly including 40 wt% of trimethylchlorosilane and 55 wt% of silicon tetrachloride) was dropped into 200 g of an ethanol aqueous solution (molar ratio of ethanol to water: 13:0.6) below 10 °C and reacted at below 10 °C for 1 h. During the reaction, the generated hydrogen chloride gas was continuously discharged. After the reaction, the temperature was raised to 60 °C for distillation and then refluxed for 3 h to obtain a reaction solution.

[0036] Step 2: 200 g of an ethanol aqueous solution (molar ratio of ethanol to water: 13:1.5) was dropped into the above reaction solution and reacted at below 10 °C for 1 h. During the reaction, the generated hydrogen chloride gas was continuously discharged to obtain a hydrophobic silica sol.

[0037] Step 3: Add an ethanol-alkali solution (molar ratio of ethanol, sodium hydroxide, and water is 3:1.65×10 -2 : 0.055) at a temperature below 10 °C to the above-mentioned silica sol until the pH of the silica sol reaches 4, then let it stand for 2 h for gelation. After gelation, crush the obtained gel to the micron level, and wash the gel twice with 300 ml of pure water to obtain a wet silica gel material.

[0038] Step 4: Finally, dry the wet silica gel material to obtain a superhydrophobic silica aerogel powder.

[0039] Example 2

[0040] Step 1: Drop 240 g of a chlorosilane azeotrope (40 wt% trimethylchlorosilane, 55 wt% silicon tetrachloride) into 200 g of an ethanol aqueous solution (molar ratio of ethanol to water: 13:0.4) at a temperature below 10 °C, react for 1 h at a temperature below 10 °C, continuously discharge the generated hydrogen chloride gas during the reaction, raise the temperature to 60 °C for distillation after the reaction, and then reflux for 3 h to obtain a reaction solution;

[0041] Step 2: Drop 200 g of an ethanol aqueous solution (molar ratio of ethanol and water is 13:1) into the above reaction solution, react for 1 h at a temperature below 10 °C, and continuously discharge the generated hydrogen chloride gas during the reaction to obtain a hydrophobic silica sol;

[0042] Step 3: Add an ethanol-alkali solution (molar ratio of ethanol, sodium hydroxide, and water is 3:1.65×10 -2 : 0.055) at a temperature below 10 °C to the above-mentioned silica sol until the pH of the silica sol reaches 4, then let it stand for 2 h for gelation. After gelation, crush the obtained gel to the micron level, and wash the gel twice with 300 ml of pure water to obtain a wet silica gel material;

[0043] Step 4: Finally, dry the wet silica gel material to obtain a superhydrophobic silica aerogel powder.

[0044] Example 3

[0045] Step 1: Drop 240 g of a chlorosilane azeotrope (40 wt% trimethylchlorosilane, 55 wt% silicon tetrachloride) into 200 g of an ethanol aqueous solution (molar ratio of ethanol to water is 13:0.8) at a temperature below 10 °C, react for 1 h at a temperature below 10 °C, continuously discharge the generated hydrogen chloride gas during the reaction, raise the temperature to 60 °C for distillation after the reaction, and then reflux for 3 h to obtain a reaction solution;

[0046] Step 2: Add 200 g of an ethanol aqueous solution (molar ratio of ethanol to water is 13:1.0) dropwise to the above reaction solution, react at a temperature below 10 °C for 1 h, continuously discharge the generated hydrogen chloride gas during the reaction process to obtain a hydrophobic silica sol;

[0047] Step 3: Add an ethanol alkali solution (molar ratio of ethanol, sodium hydroxide, and water is 3:1.65×10 -2 :0.055) at a temperature below 10 °C to the above silica sol until the pH of the silica sol reaches 4, then let it stand for 2 h for gelation. After gelation, crush the obtained gel to the micron level and wash the gel twice with 300 ml of pure water to obtain a wet silica gel material;

[0048] Step 4: Finally, dry the wet silica gel material to obtain a superhydrophobic silica aerogel powder.

[0049] Example 4

[0050] Step 1: Add 240 g of a chlorosilane azeotrope (40 wt% trimethylchlorosilane, 55 wt% silicon tetrachloride) dropwise to 200 g of an ethanol aqueous solution (molar ratio of ethanol to water is 13:0.6) at a temperature below 10 °C, react at a temperature below 10 °C for 1 h, continuously discharge the generated hydrogen chloride gas during the reaction process, then raise the temperature to 60 °C for distillation after the reaction, and then reflux for 3 h to obtain a reaction solution;

[0051] Step 2: Add 200 g of an ethanol aqueous solution (molar ratio of ethanol to water is 13:1.5) dropwise to the above reaction solution, react at a temperature below 10 °C for 1 h, continuously discharge the generated hydrogen chloride gas during the reaction process to obtain a hydrophobic silica sol;

[0052] Step 3: Add an ethanol alkali solution (molar ratio of ethanol, sodium hydroxide, and water is 3:1.65×10 -2 :0.055) at a temperature below 10 °C to the above silica sol until the pH of the silica sol reaches 4, then let it stand for 2 h for gelation. After gelation, crush the obtained gel to the micron level and wash the gel twice with 300 ml of pure water;

[0053] Add a glass fiber mat to the above silica sol for full impregnation, let it stand for 2 h for gelation, and after gelation, perform solvent replacement in water and n-hexane successively to obtain a wet silica gel material;

[0054] Step 4: Finally, dry the wet silica gel material to obtain a silica aerogel mat.

[0055] Comparative Example 1

[0056] Step 1: 240 g of chlorosilane azeotrope (40 wt% trimethylchlorosilane, 45 wt% silicon tetrachloride) was added dropwise to 200 g of an alcohol aqueous solution at 10°C (molar ratio of ethanol to water is 13:0.6). The reaction was carried out at 15°C for 1 h, then the temperature was raised to 60°C for distillation, and then refluxed for 3 h. During the reaction, the generated hydrogen chloride gas was continuously discharged.

[0057] Step 2: 200 g of an alcohol aqueous solution (molar ratio of ethanol to water is 13:1.5) was added dropwise to the above reaction solution. The reaction was carried out at 10°C for 1 h, and the generated hydrogen chloride gas was continuously discharged during the reaction to obtain a hydrophobic silica sol.

[0058] Step 3: An alcohol-alkali solution at 10°C (molar ratio of ethanol, alkali, and water is 3:1.65×10 -2 :0.055) was added to the above silica sol until the pH of the silica sol reached 4, and then it was left standing for 2 h for gelation. After gelation, the obtained gel was crushed into micron-sized particles and washed twice with 300 ml of pure water to obtain a wet silica gel material.

[0059] Step 4: Finally, the wet silica gel material was dried to obtain a superhydrophobic silica aerogel material.

[0060] Comparative Example 2

[0061] Step 1: 240 g of chlorosilane azeotrope (40 wt% trimethylchlorosilane, 55 wt% silicon tetrachloride) was added dropwise to 200 g of an ethanol aqueous solution below 10°C (molar ratio of ethanol to water: 13:1.5). The reaction was carried out below 10°C for 1 h, and the generated hydrogen chloride gas was continuously discharged during the reaction. After the reaction, the temperature was raised to 60°C for distillation, and then refluxed for 3 h to obtain a reaction solution.

[0062] Step 2: 200 g of an ethanol aqueous solution (molar ratio of ethanol to water: 13:0.6) was added dropwise to the above reaction solution. The reaction was carried out below 10°C for 1 h, and the generated hydrogen chloride gas was continuously discharged during the reaction to obtain a hydrophobic silica sol.

[0063] Step 3: An ethanol-alkali solution below 10°C (molar ratio of ethanol, sodium hydroxide, and water is 3:1.65×10 -2 :0.055) was added to the above silica sol until the pH of the silica sol reached 4, and then it was left standing for 2 h for gelation. After gelation, the obtained gel was crushed to the micron level, washed twice with 300 ml of pure water to obtain a wet silica gel material.

[0064] Step 4: Finally, the wet silica gel material was dried to obtain a superhydrophobic silica aerogel powder.

[0065] Test Results

[0066] The performance of the silica aerogel materials prepared in the above examples and comparative examples was tested, and the results are shown in the following table.

[0067] Table 1 Performance test of superhydrophobic silica in examples and comparative examples

[0068]

[0069] It can be seen from the above test results that the superhydrophobic silica aerogel prepared in the examples of the present invention has a relatively large specific surface area, a relatively small thermal conductivity, good heat insulation performance, a relatively large hydrophobic angle, a relatively small rolling angle, and good superhydrophobicity. In the comparative examples of the present invention, due to the relatively high reaction temperature, and the large difference in the hydrolysis rates of silicon tetrachloride and trimethylchlorosilane in the chlorosilane azeotrope, the polymerization rate is relatively fast after the hydrolysis of silicon tetrachloride, the gel effect is poor, and it is impossible to achieve hydrophobization well, and the heat insulation and hydrophobic effects of the prepared aerogel are poor.

Claims

1. A preparation method of a superhydrophobic silica aerogel material, characterized in that, It includes the following steps: Step 1: Drop the chlorosilane azeotrope into the aqueous alcohol solution for reaction, continuously discharge the generated hydrogen chloride during the reaction, and separate ethanol and hydrogen chloride after the reaction to obtain a reaction solution. The molar ratio of alcohol to water in the aqueous alcohol solution is 10-13:0.4-0.8; Step 2: Drop another aqueous alcohol solution into the reaction solution for reaction again, continuously discharge the generated hydrogen chloride gas during the reaction to obtain a hydrophobic silica sol. The molar ratio of alcohol to water in the other aqueous alcohol solution is 10-13:1-2; Step 3: Add an alcoholic alkali solution to the hydrophobic silica sol and stir evenly, then let it stand for gelation. After gelation, wash it to obtain a wet silica gel material; Step 4: Dry it to obtain a superhydrophobic silica aerogel material.

2. The preparation method of the superhydrophobic silica aerogel material according to claim 1, characterized in that, In the chlorosilane azeotrope in Step 1, the content of trimethylchlorosilane is 40-60 wt%, and the content of silicon tetrachloride is 30-55 wt%.

3. The preparation method of the superhydrophobic silica aerogel material according to claim 1, characterized in that, The mass ratio of the aqueous alcohol solution dropped twice in Step 1 and Step 2 to the chlorosilane azeotrope is 0.8-1.6:1; the reaction temperature in Step 1 and Step 2 is 0-10 °C.

4. The preparation method of the superhydrophobic silica aerogel material according to claim 3, characterized in that, The mass of water in the aqueous alcohol solution added in Step 1 is less than the mass of water in the aqueous alcohol solution added in Step 2; the alcohol selected is methanol, ethanol, or ethylene glycol.

5. The preparation method of the superhydrophobic silica aerogel material according to claim 1, characterized in that, The alcohol-alkali solution described in Step 3 is a mixed solution of alcohol, alkali and water, and the molar ratio of the alcohol, alkali and water is 2~4:3×10 -3 ~3×10 -2 :0.01~0.1; the alcohol is selected from methanol, ethanol or ethylene glycol.

6. The preparation method of the superhydrophobic silica aerogel material according to claim 1, characterized in that, In Step 3, add the alcoholic alkali solution until the pH of the silica sol is 3.5-5.

7. The preparation method of the superhydrophobic silica aerogel material according to claim 1, characterized in that, In Step 3, after adding the alcoholic alkali solution to the silica sol and stirring evenly, add a fiber material and fully impregnate it, then let it stand for gelation. After gelation, perform solvent replacement to obtain a wet silica gel material.

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