A hydrophobic aerogel and its green preparation method

Abstract

This invention belongs to the field of aerogel materials technology, specifically relating to a hydrophobic aerogel and its green preparation method. The method includes the following steps: S1, adding a silicon source to a first solvent and undergoing a hydrolysis reaction to obtain a hydrolysate; S2, adding an alkaline catalyst to the hydrolysate and undergoing a condensation reaction to obtain a wet gel; S3, aging the wet gel and then adding it to a second solvent for aging and displacement to obtain an aged wet gel; S4, adding an alkaline modifying solution to the aged wet gel and undergoing a modification reaction to obtain a modified gel; S5, drying the modified gel to obtain the hydrophobic aerogel. This method significantly shortens the production cycle through process integration; and it eliminates the need for acidic modifiers in the hydrophobic modification process, greatly improving hydrophobicity and completely avoiding chloride ion residue while ensuring the basic physicochemical properties of the aerogel. The prepared hydrophobic aerogel exhibits excellent comprehensive performance and can be widely used in chemical pipelines, construction, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of aerogel materials technology, specifically relating to a hydrophobic aerogel and its green preparation method. Background Technology

[0002] Aerogels have become an important area of ​​research in materials science in recent years. As an ultralight, porous material with a three-dimensional network structure, aerogels exhibit excellent properties in thermal, mechanical, building, and chemical pipeline applications due to their extremely low density, high porosity, and large specific surface area, especially in thermal insulation materials. However, traditional aerogel preparation processes typically use acidic modifiers, which present problems such as strong corrosivity, high toxicity, and environmental pollution, significantly increasing the production cost of aerogels.

[0003] Against this backdrop, developing green, environmentally friendly, and corrosion-resistant aerogel preparation methods has become a current research hotspot. Currently, the preparation of traditional silica aerogels typically involves key steps such as hydrolysis, polycondensation, aging, solvent replacement, surface modification, and drying. Among these, the surface modification stage often employs acidic modifiers.

[0004] For example, patent document CN103936018B discloses a method for preparing hydrophobic SiO2 aerogel by atmospheric pressure drying. The method involves mixing and stirring an organosilicon source, water, and anhydrous ethanol in a specific ratio. A two-step acid-base method is used, adding acidic catalysts such as hydrochloric acid, oxalic acid, or hydrofluoric acid, and an alkaline catalyst respectively, to adjust the pH value and form a gel. After aging, the gel undergoes solvent replacement and surface hydrophobic modification treatment, replacing the hydrophilic groups on the gel surface with hydrophobic groups, thus making the gel hydrophobic. Finally, after atmospheric pressure drying, the hydrophobic SiO2 aerogel is obtained. Patent document CN104556063A discloses a low-cost method for preparing hydrophobic silica aerogel, comprising the following steps: (1) mixing organosilicate, inorganic silicate and water, adjusting the pH of the mixture system to 2-11 with acid, and allowing it to stand to gel, forming a hydrogel; (2) washing the hydrogel in tap water to reduce the salt content in the hydrogel, and then immersing the hydrogel in a surfactant aqueous solution, maintaining the system temperature at 20-90℃; (3) subjecting the hydrogel to normal pressure drying, vacuum drying or freeze drying. Patent document CN113603452A discloses a method for preparing a silica aerogel composite material, comprising the following steps: S10, providing a gel composite material; S20, placing the gel composite material in a reaction vessel for static aging; S30, introducing an acidic solution and a silsesquioxane solution into the reaction vessel, extracting the solution from the bottom of the reaction vessel, and injecting it from the top of the reaction vessel to form a circulation, thereby obtaining a modified wet gel composite material; S40, drying the wet gel composite material to obtain a hydrophobic hybrid silica aerogel composite material.

[0005] Although acid modifiers can help improve the structural properties of aerogels, their strong acidity can easily cause corrosion of chemical pipelines and shorten the service life of related building facilities in practical applications, thereby increasing the maintenance and replacement costs of equipment and restricting its industrial promotion and application.

[0006] Therefore, developing a method for preparing silica aerogels without using acidic modifiers has significant research value and application prospects, and has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] Based on this, the purpose of this invention is to provide a green preparation method for hydrophobic aerogels. This method does not use acidic modifiers, but uses an alkaline catalyst combined with silane-based modifiers for hydrophobic modification. The reaction conditions are mild, the modification process is non-corrosive, green and safe, and the modification effect is stable.

[0008] This invention also provides a hydrophobic aerogel product prepared using this green preparation method. This product has excellent comprehensive properties, including low density, ultra-low thermal conductivity, high specific surface area, large pore volume, suitable pore size, high hydrophobicity, and no chloride ion residue. It can be widely used in chemical pipelines, construction and other fields.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a green method for preparing hydrophobic aerogels, comprising the following steps: S1, add the silicon source to the first solvent and hydrolyze to obtain the hydrolysate; S2, add the alkaline catalyst to the hydrolysate described in S1 and obtain wet gel by polycondensation reaction; The wet gels described in S3 and S2 are aged and then added to a second solvent for aging and displacement to obtain aged wet gels. S4, the modified liquid is added to the aged wet gel described in S3, and the modified gel is obtained after the modification reaction; The modified gels described in S5 and S4 are dried to obtain the hydrophobic aerogel.

[0010] Further, the mass ratio of the silicon source to the first solvent in S1 is 1:2~2.2; the silicon source includes methyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS) or polyethyl orthosilicate (Si40), and the first solvent includes methanol, ethanol or tert-butanol; the conditions for the hydrolysis reaction are: atmospheric pressure, temperature of 25±5℃, and time of 7~9h; after the reaction is completed, it is stored at 6~8℃.

[0011] Further, the alkaline catalyst in S2 includes 0.8~1.2 mol / L ammonia water or 0.8~1.2 mol / L NaOH aqueous solution; the mass of the alkaline catalyst added is 5~7% of the mass of the hydrolysate; the conditions for the polycondensation reaction are: atmospheric pressure, temperature of 25±5℃, and time of 8~12s.

[0012] Furthermore, the aging conditions of the wet gel in S3 are: normal pressure, temperature of 25±5℃, and time of 8~12min; the volume ratio of the wet gel to the second solvent is 1:(2~8).

[0013] Furthermore, the second solvent in S3 includes ethanol, n-hexane, isooctane, or isopropanol; the number of replacements is 3 to 5 times, and the time for each replacement is 6 to 10 hours.

[0014] Furthermore, the modified liquid in S4 is composed of a hydrophobic modifier, an alkaline catalyst and a third solvent, and the mass ratio of the hydrophobic modifier, the alkaline catalyst and the third solvent is (1~3):1:(6~8); the volume ratio of the aged wet gel to the modified liquid is 1:(2~8).

[0015] Further, the hydrophobic modifier includes hexamethyldisiloxane, trimethylsilanol, trimethylethoxysilane, or trimethylmethoxysilane; the third solvent includes ethanol, n-hexane, isooctane, or isopropanol; and the alkaline catalyst includes 0.8-1.2 mol / L ammonia or 0.8-1.2 mol / L NaOH aqueous solution.

[0016] Furthermore, the conditions for the modification reaction described in S4 are: temperature of 50~70℃ and time of 7~9h.

[0017] Furthermore, the drying described in S5 is supercritical drying, and the conditions for supercritical drying are: temperature 45~70℃, pressure 7~15MPa, and time 7~9h.

[0018] This invention also provides a hydrophobic aerogel, prepared using the above-described green preparation method for hydrophobic aerogels. Preferably, the density of the hydrophobic aerogel is 70-75 kg / m³. 3 Its thermal conductivity is no higher than 0.022 W / (m·K), and its specific surface area is 750~890 m². 2 / g, pore volume is 5.0~7.0cm³ / g, pore size is 20~25nm, water contact angle is 140°~160°, and chloride ion content is 0ppm.

[0019] The beneficial effects of this invention are: 1. The present invention provides a green preparation method for hydrophobic aerogels, with an environmentally friendly and efficient modification system. The present invention uses an alkaline catalyst and ethanol in combination with silane-based modifying agents for hydrophobic modification, overcoming the technical challenge that traditional acidic modifiers easily cause corrosion of chemical pipelines and shorten the service life of related building facilities, thereby increasing equipment maintenance and replacement costs and hindering their industrial promotion and application.

[0020] 2. The hydrophobic aerogel provided by the present invention has excellent comprehensive properties such as low density, ultra-low thermal conductivity, high specific surface area, large pore volume, suitable pore size, high hydrophobicity and no chloride ion residue, and can be widely used in chemical pipelines, construction and other fields. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. All mentioned embodiments are implemented based on the technical solutions of the present invention, and detailed implementation processes are given. However, it should be stated that the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials; and unless otherwise specified, the room temperature or room temperature refers to 25±5℃.

[0022] Example 1

[0023] A green method for preparing hydrophobic aerogels, comprising the following steps: S1: At room temperature and pressure, 152 kg of TMOS and 320 kg of methanol were reacted in a reactor for 8 hours. After the reaction was completed, the mixture was stored at a low temperature of 7°C to obtain the hydrolysate.

[0024] S2: At room temperature and pressure, add 24 kg of 1 mol / L ammonia water to the hydrolysate obtained in step S1, stir in the reactor for 10 s, and after the reaction is completed, wait for it to gel to obtain wet gel. Run on the conveyor belt for 10 min to complete the aging.

[0025] S3: After aging, 500 kg of ethanol is added to the reactor for aging and replacement. Each replacement lasts for 8 hours, and the replacement is completed after 3 replacements.

[0026] S4: After the replacement is completed, mix 100 kg of hexamethyldisiloxane, 50 kg of 1 mol / L ammonia water and 350 kg of ethanol evenly, add them to the reactor, and modify at 60℃ for 8 hours to complete the modification.

[0027] S5: After modification, the wet gel is placed in a supercritical drying device for supercritical drying for 8 hours (temperature 60℃, pressure 10MPa) to obtain a hydrophobic aerogel.

[0028] Example 2

[0029] A green method for preparing hydrophobic aerogels, comprising the following steps: S1: At room temperature and pressure, 152 kg of TMOS and 320 kg of methanol were reacted in a reactor for 8 hours. After the reaction was completed, the mixture was stored at a low temperature of 7°C to obtain the hydrolysate.

[0030] S2: At room temperature and pressure, add 24 kg of 1 mol / L ammonia water to the hydrolysate obtained in step S1, stir in the reactor for 10 s, and after the reaction is completed, wait for it to gel to obtain wet gel. Run on the conveyor belt for 10 min to complete the aging.

[0031] S3: After aging, 500 kg of ethanol is added to the reactor for aging and replacement. Each replacement lasts for 8 hours, and the replacement is completed after 3 replacements.

[0032] S4: After the replacement is completed, 100 kg of hexamethyldisiloxane, 50 kg of 1 mol / L NaOH aqueous solution and 350 kg of ethanol are mixed evenly and added to the reactor. The modification is completed at 60℃ for 8 hours.

[0033] S5: After modification, the wet gel is placed in a supercritical drying device for supercritical drying for 8 hours (temperature 60℃, pressure 10MPa) to obtain a hydrophobic aerogel.

[0034] Comparative Example 1 A method for preparing a hydrophobic aerogel, comprising the following steps: S1: At room temperature and pressure, 152 kg of TMOS and 320 kg of methanol were reacted in a reactor for 8 hours. After the reaction was completed, the mixture was stored at a low temperature of 7°C to obtain the hydrolysate.

[0035] S2: At room temperature and pressure, add 24 kg of 1 mol / L ammonia water to the hydrolysate obtained in step S1, stir in the reactor for 10 s, and after the reaction is completed, wait for it to gel to obtain wet gel. Run on the conveyor belt for 10 min to complete the aging.

[0036] S3: After aging, 500 kg of ethanol is added to the reactor for aging and replacement. Each replacement lasts for 8 hours, and the replacement is completed after 3 replacements.

[0037] S4: After the replacement is completed, mix 100 kg of hexamethyldisiloxane and 350 kg of ethanol evenly, add them to the reactor, and modify at 60°C for 8 hours to complete the modification.

[0038] S5: After modification, the wet gel is placed in a supercritical drying device for supercritical drying for 8 hours (temperature 60℃, pressure 10MPa) to obtain a hydrophobic aerogel.

[0039] Comparative Example 2 A method for preparing a hydrophobic aerogel, comprising the following steps: S1: At room temperature and pressure, 152 kg of TMOS and 320 kg of methanol were reacted in a reactor for 8 hours. After the reaction was completed, the mixture was stored at a low temperature of 7°C to obtain the hydrolysate.

[0040] S2: At room temperature and pressure, add 24 kg of 1 mol / L ammonia water to the hydrolysate obtained in step S1, stir in the reactor for 10 s, and after the reaction is completed, wait for it to gel to obtain wet gel. Run on the conveyor belt for 10 min to complete the aging.

[0041] S3: After aging, 500 kg of ethanol is added to the reactor for aging and replacement. Each replacement lasts for 8 hours, and the replacement is completed after 3 replacements.

[0042] S4: After the replacement is completed, mix 100 kg of hexamethyldisiloxane, 1 kg of concentrated hydrochloric acid and 350 kg of ethanol evenly, add them to the reactor, and modify at 60°C for 8 hours to complete the modification.

[0043] S5: After modification, the material in the stirred tank is repeatedly washed with isooctane to remove excess liquid.

[0044] S6: Place the wet gel in a supercritical drying device for supercritical drying for 8 hours (temperature 60℃, pressure 10MPa) to obtain a hydrophobic aerogel.

[0045] Comparative Example 3 A method for preparing a hydrophobic aerogel, comprising the following steps: S1: At room temperature and pressure, 152 kg of TMOS and 320 kg of methanol were reacted in a reactor for 8 hours. After the reaction was completed, the mixture was stored at a low temperature of 7°C to obtain the hydrolysate.

[0046] S2: At room temperature and pressure, add 24 kg of 1 mol / L ammonia water to the hydrolysate obtained in step S1, stir in the reactor for 10 s, and after the reaction is completed, wait for it to gel to obtain wet gel. Run on the conveyor belt for 10 min to complete the aging.

[0047] S3: After aging, 500 kg of ethanol is added to the reactor for aging and replacement. Each replacement lasts for 8 hours, and the replacement is completed after 3 replacements.

[0048] S4: After the replacement is completed, mix 100 kg of trimethylchlorosilane and 400 kg of ethanol evenly, add them to the reactor, and modify at 60°C for 8 hours to complete the modification.

[0049] S5: After modification, the material in the stirred tank is repeatedly washed with isooctane to remove excess liquid.

[0050] S6: Place the wet gel in a supercritical drying device for supercritical drying for 8 hours (temperature 60℃, pressure 10MPa) to obtain a hydrophobic aerogel.

[0051] Implementation effect analysis

[0052] The density, thermal conductivity, specific surface area, pore volume, pore size, water contact angle, and chloride ion content of the aerogel products prepared in Examples 1-2 and Comparative Examples 1-3 were tested respectively. The test results are shown in Table 1 below.

[0053] Table 1. Summary of the properties of the aerogel products prepared in Examples 1-2 and Comparative Examples 1-3

[0054] As can be seen from the data in Table 1, the hydrophobic aerogel prepared by the green preparation method of the present invention achieves improved hydrophobic properties while maintaining stable basic properties such as density, thermal conductivity, and specific surface area. At the same time, it has no chloride ion residue and has both excellent performance and environmental friendliness.

[0055] In summary, this invention abandons the hydrophobic modification process of acidic modifiers. While ensuring the basic physicochemical properties of aerogel, it improves hydrophobic properties and avoids chloride ion residue. It overcomes the technical difficulties that traditional acidic modifiers can easily cause corrosion of chemical pipelines and shorten the service life of related building facilities, thereby increasing the maintenance and replacement costs of equipment and restricting its industrial promotion and application.

[0056] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A green preparation method for hydrophobic aerogels, characterized in that, Includes the following steps: S1, add the silicon source to the first solvent and hydrolyze to obtain the hydrolysate; S2, add the alkaline catalyst to the hydrolysate described in S1 and obtain a wet gel through a polycondensation reaction; The wet gels described in S3 and S2 are aged and then added to a second solvent for aging and displacement to obtain aged wet gels. S4, the modified liquid is added to the aged wet gel described in S3, and the modified gel is obtained after the modification reaction; The modified gels described in S5 and S4 are dried to obtain the hydrophobic aerogel.

2. The green preparation method of the hydrophobic aerogel according to claim 1, characterized in that, The mass ratio of the silicon source to the first solvent in S1 is 1:2~2.2; the silicon source includes methyl orthosilicate, ethyl orthosilicate or polyethyl orthosilicate, and the first solvent includes methanol, ethanol or tert-butanol; the conditions for the hydrolysis reaction are: atmospheric pressure, temperature of 25±5℃, and time of 7~9h; after the reaction is completed, it is stored at 6~8℃.

3. The green preparation method of the hydrophobic aerogel according to claim 1, characterized in that, The alkaline catalyst in S2 includes 0.8~1.2 mol / L ammonia or 0.8~1.2 mol / L NaOH aqueous solution; the mass of the alkaline catalyst added is 5~7% of the mass of the hydrolysate; the conditions for the polycondensation reaction are: atmospheric pressure, temperature 25±5℃, and time 8~12s.

4. The green preparation method of the hydrophobic aerogel according to claim 1, characterized in that, The aging conditions of the wet gel in S3 are: normal pressure, temperature of 25±5℃, and time of 8~12min; the volume ratio of the wet gel to the second solvent is 1:(2~8).

5. The green preparation method of the hydrophobic aerogel according to claim 1, characterized in that, The second solvent in S3 includes ethanol, n-hexane, isooctane, or isopropanol; the number of replacements is 3 to 5, and the time for each replacement is 6 to 10 hours.

6. The green preparation method of the hydrophobic aerogel according to claim 1, characterized in that, The modified liquid in S4 is composed of a hydrophobic modifier, an alkaline catalyst and a third solvent, and the mass ratio of the hydrophobic modifier, the alkaline catalyst and the third solvent is (1~3):1:(6~8); the volume ratio of the aged wet gel to the modified liquid is 1:(2~8).

7. The green preparation method of the hydrophobic aerogel according to claim 6, characterized in that, The hydrophobic modifier includes hexamethyldisiloxane, trimethylsilanol, trimethylethoxysilane, or trimethylmethoxysilane; the third solvent includes ethanol, n-hexane, isooctane, or isopropanol.

8. The green preparation method of the hydrophobic aerogel according to claim 1, characterized in that, The conditions for the modification reaction described in S4 are: temperature of 50~70℃ and time of 7~9h.

9. The green preparation method of the hydrophobic aerogel according to claim 1, characterized in that, The drying described in S5 is supercritical drying, and the conditions for supercritical drying are: temperature 45~70℃, pressure 7~15MPa, and time 7~9h.

10. A hydrophobic aerogel, characterized in that, The hydrophobic aerogel was prepared using the green preparation method according to any one of claims 1 to 9.

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