Preparation method of high-temperature-resistant hydrophobic aerogel based on polyion liquid modification

Abstract

The invention discloses a preparation method of polyion liquid modification-based high-temperature-resistant hydrophobic aerogel, which comprises the following specific steps: reacting a silicon source, an acid catalyst and an alcohol solvent at 30-65 DEG C for 2-8 hours to obtain silica sol, and adjusting the pH value of the silica sol to 3-6; mixing the obtained silica sol with a basic catalyst to obtain a mixed solution, and adjusting the pH value of the mixed solution to 6.7-9; compounding the obtained mixed solution with a base material, and standing at room temperature for 4-150 minutes, so that the silicon dioxide sol is gelatinized to form composite wet gel; soaking the composite wet gel in an alcohol solvent, aging for 5-24 hours at the temperature of 40-65 DEG C, and drying in a carbon dioxide supercritical extraction kettle after aging is completed, so as to finally obtain the silicon dioxide high-temperature-resistant hydrophobic aerogel felt.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic materials, and in particular to a method for preparing a high-temperature resistant hydrophobic aerogel modified by polyionic liquid. Background Art

[0002] Silica aerogel insulation composite materials have been widely used in the fields of thermal insulation and heat preservation such as aerospace and petrochemical industry. Since the surface of silica aerogel contains a large number of hydroxyl groups (-OH), it is easy to absorb moisture in a humid environment, resulting in an increase in thermal conductivity and a decrease in thermal insulation performance. Therefore, the preparation of hydrophobic aerogel is an effective way to solve this problem. Researchers used hydrophobic modifiers such as methyltrimethoxysilane, trimethylchlorosilane, dimethylchlorosilane and hexamethyldisilazane to prepare hydrophobic silica aerogel and its thermal insulation composite materials through in-situ method and surface post-treatment method. However, these commonly used hydrophobic modifiers have the problems of low boiling point, flammability, toxicity and poor operating safety. In contact with air or during modification, toxic and harmful gases such as HCl and NH3 will be released. In the fields of aerospace and petrochemical industry, silica aerogel insulation composite materials still need to maintain good hydrophobic properties at higher temperatures. The current preparation process of hydrophobic aerogel is relatively complicated, and the temperature resistance of the hydrophobic group needs to be improved. It is urgent to develop aerogel insulation composite materials that can maintain hydrophobic properties at higher temperatures. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for preparing a high-temperature resistant hydrophobic aerogel based on polyionic liquid modification, so as to solve the problems of the prior art hydrophobic aerogel having complex preparation process, poor high temperature resistance, and release of toxic and harmful gases during contact with air or modification.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A method for preparing a high temperature resistant hydrophobic aerogel modified by polyionic liquid, the specific steps are as follows:

[0006] Step 1: reacting a silicon source, an acidic catalyst, and an alcohol solvent at 30-65° C. for 2-8 hours to obtain a silica sol, and adjusting the pH value of the silica sol to 3-6; wherein the molar ratio of the silicon source, the acidic catalyst, and the alcohol solvent is (5-6):15:(90-110);

[0007] Step 2: mixing the silica sol obtained in step 1 with an alkaline catalyst to obtain a mixed solution, and adjusting the pH value of the mixed solution to 6.7-9; the molar ratio of the silica sol to the alkaline catalyst is 100:(0.5-1.5);

[0008] Step 3: Compounding the mixed solution obtained in step 2 with a substrate, standing at room temperature for 4-150 minutes to gel the silica sol to form a composite wet gel; the volume ratio of the mixed solution to the substrate is (1-1.5):1;

[0009] Step 4: soaking the composite wet gel obtained in step 3 in an alcohol solvent, aging at 40-65° C. for 5-24 hours, and placing it in a carbon dioxide supercritical extraction kettle for drying after aging, and finally obtaining a silica high temperature resistant hydrophobic aerogel felt;

[0010] wherein at least one hydrophobic modifier is added to the silicon source in step 1; and / or, in step 3, at least one hydrophobic modifier is added after the composite wet gel is immersed in an alcohol solvent; the hydrophobic modifier is one or more of poly R-vinylsilane imidazole ionic liquid, poly R-propylenesilane ionic liquid, poly R-based siloxane ionic liquid, wherein R is C 1～20 Alkyl carbon chain; calculated by volume percentage, the total volume of the hydrophobic modifier added accounts for 1 to 10% of the volume of the alcohol solvent.

[0011] Preferably, the silicon source is one or more of methyl orthosilicate, ethyl orthosilicate, methyltrimethoxysilane and methyltriethoxysilane.

[0012] Preferably, the acidic catalyst is one or more of hydrochloric acid, oxalic acid, citric acid, nitric acid, and acetic acid; and the concentration of the acidic catalyst is 0.01 to 1 mol / L.

[0013] Preferably, the alkaline catalyst is one or more of ammonia water, sodium hydroxide and potassium hydroxide; the concentration of the alkaline catalyst is 0.01-5 mol / L.

[0014] Preferably, the alcohol solvent is one or more of methanol, ethanol and propanol.

[0015] Preferably, the hydrophobicity of the high temperature resistant hydrophobic silica aerogel felt is less than 4%.

[0016] Preferably, the thermal conductivity of the high temperature resistant hydrophobic silica aerogel felt is less than 0.055 W / (m·K) at 600°C.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. After in-depth research on the preparation method of hydrophobic aerogel, the present invention unexpectedly found that the use of poly (R-vinyl silane imidazole) ionic liquid, poly (R-propylene silane) ionic liquid or poly (R-based siloxane) ionic liquid as a hydrophobic modifier, because these compounds contain long-chain alkyl (C 1～20), which makes the modified aerogel felt have extremely low mass water absorption (less than 4%). The aerogel felt not only has excellent hydrophobic properties at room temperature, but also maintains excellent hydrophobic properties even in a high humidity environment.

[0019] 2. The present invention also found that after the polyionic liquid is introduced through the preparation method, the polyionic liquid has a higher boiling point, which means that they can maintain the integrity of the chemical structure at higher temperatures without decomposing. This property also makes the obtained aerogel felt have extremely excellent high temperature resistance and can withstand high temperatures of about 600°C for a long time without losing function. This is very important for application scenarios that require strict thermal insulation protection, such as aerospace, industrial furnace linings, and automotive exhaust systems.

[0020] 3. When introducing polyionic liquid, the preparation method of the present invention effectively enhances the connection points of the internal network structure of the aerogel through the strong interaction force between the polyionic liquid molecules, thereby improving the overall mechanical properties of the aerogel, so that the prepared aerogel felt has greater flexibility and compressive strength (up to 5MPa); at the same time, by adjusting the type and proportion of polyionic liquid used in the preparation process, the microstructure of the obtained aerogel felt, including the pore size and distribution, can also be controlled, so that the high temperature resistance of the aerogel felt is further improved. DETAILED DESCRIPTION

[0021] The present invention will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the present invention belong to the scope of protection of the present invention.

[0022] Unless otherwise indicated in specific cases in the present invention, the numerical ranges listed herein include the upper and lower limits, and all integers and fractions within the range, and are not limited to the specific values ​​listed when defining the range.

[0023] 1. A method for preparing high temperature resistant hydrophobic aerogel modified by polyionic liquid

[0024] Step 1: reacting a silicon source, an acidic catalyst, and an alcohol solvent at 30-65° C. for 2-8 hours to obtain a silica sol, and adjusting the pH value of the silica sol to 3-6; wherein the molar ratio of the silicon source, the acidic catalyst, and the alcohol solvent is (5-6):15:(90-110);

[0025] Step 2: Mix the silica sol obtained in step 1 with an alkaline catalyst to obtain a mixed solution, and adjust the pH value of the mixed solution to 6.7-9; the molar ratio of the silica sol to the alkaline catalyst is 100:(0.5-1.5);

[0026] Step 3: Compounding the mixed solution obtained in step 2 with the substrate, standing at room temperature for 4-150 minutes, so that the silica sol is gelled to form a composite wet gel; the mass ratio of the mixed solution to the substrate is (1-1.5):1 by volume;

[0027] Step 4: soaking the composite wet gel obtained in step 3 in an alcohol solvent, aging at 40-65° C. for 5-24 hours, and placing it in a carbon dioxide supercritical extraction kettle for drying after aging, and finally obtaining a silica high temperature resistant hydrophobic aerogel felt;

[0028] wherein at least one hydrophobic modifier is added to the silicon source in step 1; and / or, in step 3, at least one hydrophobic modifier is added after the composite wet gel is immersed in an alcohol solvent; the hydrophobic modifier is one or more of poly R-vinylsilane imidazole ionic liquid, poly R-propylenesilane ionic liquid, poly R-based siloxane ionic liquid, wherein R is C 1～20 Alkyl carbon chain; calculated by volume percentage, the total volume of the hydrophobic modifier added accounts for 0.1 to 15% of the volume of the alcohol solvent.

[0029] The present invention found that although traditional SiO2 aerogels have the advantages of light weight, high porosity and good thermal insulation performance, they face two major challenges in practical applications: one is that they are not hydrophobic enough and easily absorb moisture in a humid environment, resulting in performance degradation; the other is that the heat resistance is limited. When the temperature exceeds a certain limit, the internal structure of the material may undergo irreversible changes, thereby affecting its long-term stability. At the same time, traditional aerogels usually exhibit poor mechanical strength, which limits their application in certain situations where they need to withstand large external forces. To this end, the present invention conceives of introducing ionic liquids into aerogel felt, thereby attempting to solve the above-mentioned technical problems. However, the present invention found that traditional ionic liquids are easy to volatilize or decompose under high temperature conditions, thereby releasing toxic and harmful gases. The present invention considers the use of polyionic liquids with higher boiling points and better thermal stability, especially those with long-chain alkyl groups (C 1～20) as a hydrophobic modifier, which can not only effectively reduce the surface energy of aerogels and reduce water adsorption, but also maintain stable hydrophobic properties even under high temperature conditions due to its special chemical structure. More importantly, this material maintains its physical and chemical properties unchanged over a wide temperature range, thereby ensuring that the modified aerogel can continue to work without failure in extreme environments. After introducing the polyionic liquid, the present invention also unexpectedly discovered that due to the addition of the polyionic liquid, a large number of ionic bonds are formed between the cations and anions in the polyionic liquid. These ionic bonds are staggered in space to form a three-dimensional network, which can further strengthen the internal network structure of the aerogel felt, increase its flexibility and compressive strength, and greatly enhance the mechanical properties of the entire system. At the same time, the introduction of the polyionic liquid can also control the microstructural characteristics of the aerogel felt, such as pore size and distribution, so as to obtain a larger specific surface area, which makes the aerogel felt have a lower thermal conductivity even under high temperature conditions, and the thermal insulation effect has been significantly improved, creating conditions for its application in more fields.

[0030] In some embodiments of the present invention, for the introduction of the hydrophobic modifier, the present invention finds that it can be introduced into the silicon source in advance, which does not affect the performance of its technical effect, and can also achieve the improvement of the hydrophobic properties, high temperature resistance and mechanical properties of the aerogel felt. Therefore, in the present invention, the hydrophobic modifier can be introduced into the silicon source in advance, or introduced during the aging treatment. These two methods can be selected or both can be used in parallel.

[0031] In some embodiments of the present invention, in step 1, the molar ratio of the silicon source, the acidic catalyst, and the alcohol solvent is (5-6):15:(90-110), for example, it can be 5:15:90, 5:15:100, 6:15:110, etc., and all ranges and sub-ranges between the above values; it should be understood that, in the implementation scheme, any of the above ranges can be combined with any other ranges.

[0032] In some embodiments of the present invention, in step 2, the molar ratio of silica sol to alkaline catalyst is 100:(0.5-1.5), for example, it can be 100:0.5, 100:1, 100:1.5, etc., and all ranges and sub-ranges between the above values; it should be understood that, in the embodiment, any of the above ranges can be combined with any other ranges.

[0033] In some embodiments of the present invention, in step 3, the volume ratio of the mixed liquid to the substrate is (1-1.5):1, ensuring that the mixed liquid fully infiltrates the substrate. For example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc., and all ranges and sub-ranges between the above values; it should be understood that, in the implementation scheme, any of the above ranges can be combined with any other ranges.

[0034] In some embodiments of the present invention, in step 4, the hydrophobic modifier is one or more of poly R-vinylsilane imidazolium ionic liquid, poly R-propylenesilane ionic liquid, and poly R-based siloxane ionic liquid, and R is a C1-20 alkyl carbon chain. The volume percentage of the hydrophobic modifier in the alcohol solvent is calculated as 1-10%. Here, the total amount of hydrophobic modifier added refers to the cumulative total amount of the modifier added to the aerogel felt. If the hydrophobic modifier is added in batches, the total amount added should be the sum of the amounts added in each batch. The amount of hydrophobic modification should not be too small, otherwise it will not play a modifying role; but it should not be too much, otherwise it will have a negative effect and cause the performance of the aerogel felt to decline. Therefore, the volume proportion of the hydrophobic modifier can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., and all ranges and sub-ranges between the above values; it should be understood that in the embodiment, any of the above ranges can be combined with any other ranges.

[0035] In some embodiments of the present invention, the silicon source is one or more of methyl orthosilicate, ethyl orthosilicate, methyltrimethoxysilane, and methyltriethoxysilane.

[0036] In some embodiments of the present invention, the acidic catalyst is one or more of hydrochloric acid, oxalic acid, citric acid, nitric acid, and acetic acid; the acidic catalyst is preferably oxalic acid, and the concentration is 0.01 to 1 mol / L.

[0037] In some embodiments of the present invention, the alkaline catalyst is one or more of ammonia water, sodium hydroxide, and potassium hydroxide; the alkaline catalyst is preferably ammonia water with a concentration of 0.01 to 5 mol / L.

[0038] In some embodiments of the present invention, the alcohol solvent is one or more of methanol, ethanol, and propanol.

[0039] In some embodiments of the present invention, the hydrophobicity of the high temperature resistant hydrophobic silica aerogel felt is less than 4%.

[0040] In some embodiments of the present invention, the thermal conductivity of the high temperature resistant hydrophobic silica aerogel felt is less than 0.055 W / (m·K) at 600°C.

[0041] 2. Examples and Comparative Examples

[0042] Example 1

[0043] A silicon source, an acidic catalyst and an alcohol solvent are reacted at 50°C for 6 hours to obtain a silica sol, and the pH value of the silica sol is adjusted to 4. After the reaction is completed, the silica sol is mixed with an alkaline catalyst, and the pH value of the silica sol is adjusted to 8. The mixed solution is then compounded with a substrate and allowed to stand at room temperature for 120 minutes to gel the silica sol to form a composite wet gel, which is then immersed in an alcohol solvent. A hydrophobic modifier is then added and aged at 55°C for 12 hours. After aging, the mixture is placed in a carbon dioxide supercritical extraction kettle for drying to finally obtain a high-temperature resistant hydrophobic aerogel felt of silica.

[0044] Table 1 (unit: mol)

[0045]

[0046] The method of Example 1 was adopted to prepare the examples and comparative examples according to the amounts of the components in Table 1.

[0047] 3. Performance Comparison

[0048] The performance tests of the embodiments and comparative examples were carried out according to the standards in Table 2, and the results are shown in Table 2.

[0049] Table 2

[0050]

[0051] From Table 1 and Table 2, we can see that:

[0052] (1) The polyionic liquid used in the present invention replaces the traditional hydrophobic modifier, which significantly improves the hydrophobic properties of the aerogel felt. The aerogel felts prepared in the examples all have extremely low mass water absorption (less than 4%), and even at room temperature and high humidity, they still maintain their excellent hydrophobic properties; while Comparative Examples 1 and 2 use commonly used hydrophobic modifiers (such as monomethyltrimethoxysilane and phenyltrimethoxysilane), and the improvement effect on the hydrophobicity of the aerogel felt is obviously not as good as that of the examples, and their hydrophobicity is higher than or equal to 4%; in particular, the hydrophobicity of Comparative Examples 4 to 5 is as high as 5.2% and 4.0%, respectively, which is significantly higher than the highest value of 3.8% in the experimental example; this shows that adding an appropriate amount of polyionic liquid as a hydrophobic modifier can indeed achieve a lower water absorption rate.

[0053] (2) The aerogel felt prepared in the embodiment has a very low thermal conductivity under high temperature environment, with a maximum value not exceeding 0.053 W / (m·K), which is significantly lower than the thermal conductivity of the comparative example. This means that the aerogel felt prepared in the embodiment has better high temperature resistance. However, due to the use of conventional hydrophobic modifiers, comparative examples 1 and 2 have higher thermal conductivity at high temperatures, and their high temperature resistance is significantly weaker than that of the embodiment. Comparative examples 4 to 5 show that the amount of polyionic liquid added has different effects on the high temperature resistance of the aerogel felt. When the amount of polyionic liquid added is not within the range described in the present invention, it will indeed have an adverse effect on the high temperature resistance of the aerogel felt. Therefore, after the polyionic liquid is introduced into the aerogel in the present invention, the aerogel felt exhibits excellent high temperature resistance and can maintain its functional integrity for a long time under continuous exposure to a high temperature environment of about 600°C.

[0054] (3) As can be seen from Table 2, in terms of compressive strength, the compressive strength of the embodiment is maintained at 4.5-5.0 MPa, which is significantly higher than that of the comparative example (1.5-3.6 MPa); at the same time, the embodiment also has a higher specific surface area (930 m 2 / g or more), which is also significantly higher than the control group (the highest is only 865m 2 / g); this fully proves that when the polyionic liquid is introduced, the strong interaction force between the polyionic liquid molecules effectively enhances the connection points of the internal network structure of the aerogel, thereby improving the overall mechanical properties of the aerogel, so that the prepared aerogel felt has greater flexibility and compressive strength (up to 5MPa); at the same time, by adjusting the type and proportion of the polyionic liquid used in the preparation process, the microstructure of the obtained aerogel felt, including the pore size and distribution, can also be controlled, so that the high temperature resistance of the aerogel felt is further improved.

[0055] (4) Comparative Example 3 uses another polyionic liquid different from the polyionic liquid described in the present invention, namely, poly R alkenyl silane imidazolium ionic liquid (R=22), but the performance of Comparative Example 3 is obviously inferior to that of the embodiment. This shows that not all polyionic liquids can achieve the technical effects described in the present invention, and other types of polyionic liquids cannot be simply replaced by the polyionic liquid described in the present invention.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a high temperature resistant hydrophobic aerogel modified by polyionic liquid, characterized in that: The specific steps are as follows: Step 1: Prepare silica sol by mixing a silicon source, an acidic catalyst and an alcohol solvent under heating conditions, and adjust the pH value of the silica sol to 3-6; wherein the molar ratio of the silicon source, the acidic catalyst and the alcohol solvent is (5-6):15:(90-110); Step 2: mixing the silica sol obtained in step 1 with an alkaline catalyst to obtain a mixed solution, and adjusting the pH value of the mixed solution to 6.7-9; the molar ratio of the silica sol to the alkaline catalyst is 100:(0.5-1.5); Step 3: Compounding the mixed solution obtained in step 2 with a substrate, standing at room temperature for 4-150 minutes to gel the silica sol to form a composite wet gel; the volume ratio of the mixed solution to the substrate is (1-1.5):1; Step 4: soaking the composite wet gel obtained in step 3 in an alcohol solvent, performing an aging treatment under heating conditions, and performing carbon dioxide supercritical extraction and drying after the aging is completed, and finally obtaining a high temperature resistant hydrophobic aerogel felt of silica; wherein at least one hydrophobic modifier is added to the silicon source in step 1; and / or, in step 3, at least one hydrophobic modifier is added after the composite wet gel is immersed in an alcohol solvent; the hydrophobic modifier is one or more of poly R-vinylsilane imidazole ionic liquid, poly R-propylenesilane ionic liquid, poly R-based siloxane ionic liquid, wherein R is C 1～20 Alkyl carbon chain; calculated by volume percentage, the total volume of the hydrophobic modifier added accounts for 0.1 to 15% of the volume of the alcohol solvent.

2. The preparation method according to claim 1, characterized in that: The silicon source is one or more of methyl orthosilicate, ethyl orthosilicate, methyltrimethoxysilane and methyltriethoxysilane.

3. The preparation method according to claim 1, characterized in that: The acidic catalyst is one or more of hydrochloric acid, oxalic acid, citric acid, nitric acid and acetic acid; the concentration of the acidic catalyst is 0.01-1 mol / L.

4. The preparation method according to claim 1, characterized in that: The alkaline catalyst is one or more of ammonia water, sodium hydroxide and potassium hydroxide; the concentration of the alkaline catalyst is 0.01-5 mol / L.

5. The preparation method according to claim 1, characterized in that: The alcohol solvent is one or more of methanol, ethanol and propanol.

6. The preparation method according to claim 1, characterized in that: The substrate is one or more of glass fiber, ceramic fiber, basalt fiber and mullite fiber.

7. The preparation method according to claim 1, characterized in that: The hydrophobicity of the silicon dioxide high temperature resistant hydrophobic aerogel felt is less than 4%.

8. The preparation method according to claim 1, characterized in that: The thermal conductivity of the silicon dioxide high temperature resistant hydrophobic aerogel felt is less than 0.055 W / (m·K) at 600°C.

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