A silica aerogel material and its preparation method

Abstract

This invention belongs to the field of silica aerogel technology, specifically relating to a silica aerogel material and its preparation method. The present invention provides a method for preparing a silica aerogel material, comprising the following steps: (1) adding water glass to sulfuric acid, and after it forms a gel, aging it in water to obtain a wet gel; (2) placing the wet gel in a modifying liquid and modifying it under heating conditions, wherein the modifying liquid includes a solvent and a modifier; (3) drying the modified wet gel to obtain a silica aerogel material. This method eliminates the need for water washing, alcohol washing, and other steps, simplifying the preparation process, avoiding the generation of large amounts of wastewater, reducing production costs, and shortening the preparation time; this method also eliminates the need for additional steps to remove Na from the water glass. + This further reduces preparation costs and shortens preparation time.

Description

Technical Field

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

[0002] The preparation of silica aerogels generally involves two steps: sol-gel method for gel preparation and gel drying to obtain the aerogel. The gel preparation process can be further divided into one-step and two-step methods. Gel drying is a crucial step in the preparation process, mainly encompassing supercritical drying technology, atmospheric pressure drying technology, and staged vacuum drying technology.

[0003] Existing atmospheric pressure drying technologies mostly use inexpensive water glass as the silicon source. To remove sodium from the water glass... + Researchers typically pre-exchange the water glass solution with ion-exchange resin or repeatedly soak and wash the resulting wet gel with water, which undoubtedly wastes a lot of time and greatly increases the preparation cost. In addition, due to the high surface tension of water, a large amount of alcohol with low surface tension is required to repeatedly exchange the wet gel with solvent, followed by surface modification, and finally drying at normal pressure.

[0004] Therefore, reducing the preparation cost and shortening the production cycle of atmospheric pressure drying technology is a major challenge in this technology. Summary of the Invention

[0005] This invention is based on the inventor's discoveries and understanding of the following facts and problems:

[0006] CN 106745003 A discloses a one-step method for rapid preparation of silica aerogel powder under normal pressure. This method uses atmospheric pressure staged drying to obtain silica aerogel powder. Although the preparation cycle is short and the obtained silica aerogel powder has good performance, this method requires solvent exchange before modifying the aerogel, which has very limited cost reduction.

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for preparing silica aerogel materials. This method eliminates the need for water washing, alcohol washing, and other steps, simplifying the preparation process, avoiding the generation of large amounts of wastewater, reducing production costs, and shortening preparation time. Furthermore, this method eliminates the need for additional steps to remove Na from water glass. + This further reduces preparation costs and shortens preparation time.

[0008] A method for preparing a silica aerogel material according to an embodiment of the present invention includes the following steps:

[0009] (1) Add water glass to sulfuric acid, wait for it to form a gel, and then put it in water for aging to obtain a wet gel.

[0010] (2) The wet gel obtained in step (1) is placed in the modification liquid and modified under heating conditions, wherein the modification liquid includes a solvent and a modifier;

[0011] (3) The modified wet gel is dried to obtain silica aerogel material.

[0012] The advantages and technical effects of the method for preparing silica aerogel materials according to embodiments of the present invention are as follows: 1. The method of the present invention involves modification under heating conditions, allowing water in the wet gel to be smoothly discharged from the pores through vigorous molecular motion. This allows the modifying liquid to enter the pores, where the modifier reacts with Si-OH to generate Si-O-Si-(CH3)3, thus completing the hydrophobic modification of the wet gel. This avoids complex and cumbersome solvent exchange steps, reduces production costs, and shortens preparation time. 2. In the method of the present invention, during the heating modification process, as water evaporates, the residual Na... + It will crystallize out as salt and eventually precipitate at the bottom of the container, eliminating the need for additional steps to remove Na from the water glass. + This further reduces the preparation cost and shortens the preparation time; 3. The method of this invention uses inexpensive and readily available water glass, resulting in low production costs and suitability for large-scale production.

[0013] In some embodiments, in step (1), the concentration of sulfuric acid is 1.8 to 3 mol / L; preferably, the volume ratio of water glass to sulfuric acid is (3.8 to 4.3):1.

[0014] In some embodiments, in step (1), the aging temperature is 40-65°C and the aging time is 2-5 hours.

[0015] In some embodiments, in step (2), the solvent comprises hexamethyldisiloxane and the modifier comprises trimethylchlorosilane.

[0016] In some embodiments, in step (2), the volume ratio of the solvent to the modifier is (20-100):1.

[0017] In some embodiments, in step (2), the volume ratio of the solvent to the wet gel is (3-6):1.

[0018] In some embodiments, in step (2), the temperature of the modification treatment is 105-130°C and the modification treatment time is 8-12h; and / or, in step (2), the heating rate is 2.5-5°C / min.

[0019] In some embodiments, in step (2), the liquid evaporated during the modification process is condensed and recovered.

[0020] In some embodiments, in step (3), the drying temperature is 110-120°C and the drying time is 2-6 hours.

[0021] This invention also provides a silica aerogel material, which is prepared using the method described above. Attached Figure Description

[0022] Figure 1 This is a flowchart of the preparation of silica aerogel material in Example 1;

[0023] Figure 2 This is the adsorption-desorption isotherm diagram of the silica aerogel material prepared in Example 2. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] A method for preparing a silica aerogel material according to an embodiment of the present invention includes the following steps:

[0026] (1) Add water glass to sulfuric acid, wait for it to form a gel, and then put it in water for aging to obtain a wet gel.

[0027] (2) The wet gel obtained in step (1) is placed in the modification liquid and modified under heating conditions, wherein the modification liquid includes a solvent and a modifier;

[0028] (3) The modified wet gel is dried to obtain silica aerogel material.

[0029] The method for preparing silica aerogel material according to this invention involves modification under heating conditions. This allows water in the wet gel to be smoothly expelled from the pores through vigorous molecular motion, enabling the modifying liquid to enter the pores. The modifier reacts with Si-OH to generate Si-O-Si-(CH3)3, thus completing the hydrophobic modification of the wet gel. This avoids complex and cumbersome solvent exchange steps, reduces production costs, and shortens the preparation time. During the heating modification process, as water evaporates, the residual Na... + It will crystallize out as salt and eventually precipitate at the bottom of the container, eliminating the need for additional steps to remove Na from the water glass. +This further reduces preparation costs and shortens preparation time; the water glass used is inexpensive and readily available, with low production costs, making it suitable for large-scale production.

[0030] In some embodiments, preferably, in step (1), the concentration of sulfuric acid is 1.8–3 mol / L; preferably, the volume ratio of water glass to sulfuric acid is (3.8–4.3):1. More preferably, in step (1), the aging temperature is 40–65°C, and the aging time is 2–5 h.

[0031] In this embodiment of the invention, the aging conditions are further optimized, under which the wet gel can better complete the aging process and reduce the time cost of preparing the aerogel.

[0032] In some embodiments, preferably, in step (2), the solvent comprises hexamethyldisiloxane and the modifier comprises trimethylchlorosilane. More preferably, in step (2), the volume ratio of the solvent to the modifier is (20-100):1.

[0033] In this embodiment of the invention, the types of solvent and modifier and their ratio are preferred, which can completely modify the wet gel without wasting the modifier. If the ratio of solvent to modifier is too small, it will waste the modifier and increase the preparation cost. If the ratio of solvent to modifier is too large, it will result in incomplete modification and thus affect the product quality.

[0034] In some embodiments, preferably, in step (2), the volume ratio of the solvent to the wet gel is (3-6):1.

[0035] In this embodiment of the invention, a preferred volume ratio of solvent to wet gel is selected, which enables rapid modification of the wet gel. If the ratio of solvent to wet gel is too small, the modification time will be too long, thereby increasing time costs. If the ratio of solvent to wet gel is too large, solvent will be wasted, thereby increasing production costs.

[0036] In some embodiments, preferably, in step (2), the temperature of the modification treatment is 105–130°C, and the modification treatment time is 8–12 h; and / or, in step (2), the heating rate is 2.5–5°C / min. More preferably, in step (2), the liquid evaporated during the modification treatment is condensed and recovered.

[0037] In this embodiment of the invention, the modification treatment temperature of 105-130°C can boil the water, allowing the water in the wet gel to be discharged from the pores more smoothly through vigorous molecular motion. This further limits the heating rate, which is beneficial for obtaining aerogel products with a complete structure. If the heating rate is too fast, the structure of the wet gel may be destroyed, resulting in pore collapse, which is not conducive to improving the adsorption performance of the aerogel product. During the modification process, a condenser is used to condense the evaporated liquid, and the condensate is returned to the oil-water separator. The upper liquid is the organic phase, and the lower liquid is the aqueous phase. The organic phase can continue to participate in the modification process, which is recycled and reduces the production cost.

[0038] In some embodiments, preferably, in step (3), the drying temperature is 110–120°C, and the drying time is 2–6 hours. More preferably, the drying process is carried out in a blower dryer.

[0039] This invention also provides a silica aerogel material, which is prepared using the method described above.

[0040] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0041] Example 1

[0042] The process for preparing silica aerogel material in this embodiment is as follows: Figure 1 As shown:

[0043] (1) Mix hexamethyldisiloxane and trimethylchlorosilane in a volume ratio of 20:1 thoroughly to prepare a modified solution, and add it to an evaporation container for later use;

[0044] (2) Slowly add water glass to dilute sulfuric acid, where the concentration of dilute sulfuric acid is 1.8 mol / L and the volume ratio of water glass to dilute sulfuric acid is 3.8:1. After it gels, put it in water for aging at a temperature of 40℃ for 5 hours.

[0045] (3) After aging, the wet gel is taken out and placed in an evaporation container containing the modified liquid, wherein the volume ratio of hexamethyldisiloxane to wet gel is 3:1; the wet gel gradually changes from light blue to yellow, and then the temperature is slowly raised to 105℃ at a heating rate of 2.5℃ / min, and the condenser is turned on to condense the evaporated liquid. The condensate is returned to the oil-water separator. As the heating time is extended, the condensed liquid will separate into layers, wherein the upper liquid is the organic phase and the lower liquid is the aqueous phase. The organic phase can be added back to the evaporation container for recycling. The heating time is 12h. After the yellow liquid in the wet gel disappears, the heating is turned off.

[0046] (4) When the temperature drops below 50°C, take out the modified wet gel and put it into a forced-air drying oven for drying. The drying temperature is 110°C and the drying time is 6 hours. After drying, the aerogel product is obtained.

[0047] Example 2

[0048] (1) Mix hexamethyldisiloxane and trimethylchlorosilane in a volume ratio of 50:1 thoroughly to prepare a modified solution, and add it to an evaporation container for later use;

[0049] (2) Slowly add water glass to dilute sulfuric acid, where the concentration of dilute sulfuric acid is 2 mol / L and the volume ratio of water glass to dilute sulfuric acid is 3.9:1. After it gels, put it in water for aging at a temperature of 50°C for 5 hours.

[0050] (3) After aging, the wet gel is taken out and placed in an evaporation container containing the modified liquid, wherein the volume ratio of hexamethyldisiloxane to wet gel is 4:1; the wet gel gradually changes from light blue to yellow, and then the temperature is slowly raised to 110°C at a heating rate of 3°C / min, and the condenser is turned on to condense the evaporated liquid. The condensate is returned to the oil-water separator. As the heating time is extended, the condensed liquid will separate into layers, wherein the upper liquid is the organic phase and the lower liquid is the aqueous phase. The organic phase can be added back to the evaporation container for recycling. The heating time is 11h. After the yellow liquid in the wet gel disappears, the heating is turned off.

[0051] (4) When the temperature drops below 50°C, take out the modified wet gel and put it into a forced-air drying oven for drying. The drying temperature is 120°C and the drying time is 3 hours. After drying, the aerogel product is obtained.

[0052] Example 3

[0053] (1) Mix hexamethyldisiloxane and trimethylchlorosilane in a volume ratio of 70:1 thoroughly to prepare a modified solution, and add it to an evaporation container for later use;

[0054] (2) Slowly add water glass to dilute sulfuric acid, where the concentration of dilute sulfuric acid is 2.5 mol / L and the volume ratio of water glass to dilute sulfuric acid is 4.1:1. After it gels, put it in water for aging at a temperature of 55°C for 4.5 h.

[0055] (3) After aging, the wet gel is taken out and placed in an evaporation container containing the modified liquid, wherein the volume ratio of hexamethyldisiloxane to wet gel is 5:1; the wet gel gradually changes from light blue to yellow, and then the temperature is slowly raised to 120°C at a heating rate of 4°C / min, and the condenser is turned on to condense the evaporated liquid. The condensate is returned to the oil-water separator. As the heating time is extended, the condensed liquid will separate into layers, wherein the upper liquid is the organic phase and the lower liquid is the aqueous phase. The organic phase can be added back to the evaporation container for recycling. The heating time is 10h. After the yellow liquid in the wet gel disappears, the heating is turned off.

[0056] (4) When the temperature drops below 50°C, take out the modified wet gel and put it into a forced-air drying oven for drying. The drying temperature is 110°C and the drying time is 4 hours. After drying, the aerogel product is obtained.

[0057] Example 4

[0058] (1) Mix hexamethyldisiloxane and trimethylchlorosilane in a volume ratio of 100:1 thoroughly to prepare a modified solution, and add it to an evaporation container for later use;

[0059] (2) Slowly add water glass to dilute sulfuric acid, where the concentration of dilute sulfuric acid is 3 mol / L and the volume ratio of water glass to dilute sulfuric acid is 4.3:1. After it gels, put it in water for aging at a temperature of 60℃ for 2 hours.

[0060] (3) After aging, the wet gel is taken out and placed in an evaporation container containing the modified liquid, wherein the volume ratio of hexamethyldisiloxane to wet gel is 3:1; the wet gel gradually changes from light blue to yellow, and then the temperature is slowly raised to 130°C at a heating rate of 5°C / min, and the condenser is turned on to condense the evaporated liquid. The condensate is returned to the oil-water separator. As the heating time is extended, the condensed liquid will separate into layers, wherein the upper liquid is the organic phase and the lower liquid is the aqueous phase. The organic phase can be added back to the evaporation container for recycling. The heating time is 8 hours. After the yellow liquid in the wet gel disappears, the heating is turned off.

[0061] (4) When the temperature drops below 50°C, take out the modified wet gel and put it into a forced-air drying oven for drying. The drying temperature is 115°C and the drying time is 3.5 hours. After drying, the aerogel product is obtained.

[0062] Comparative Example 1

[0063] (1) Slowly add water glass to dilute sulfuric acid, wherein the concentration of dilute sulfuric acid is 3 mol / L and the volume ratio of water glass to dilute sulfuric acid is 4.3:1. After it gels, put it in water for washing. The water washing temperature is 50℃, the time is 4h, and the number of water washings is 3.

[0064] (2) Then the wet gel was washed in ethanol at 50°C for 4 hours, and the number of washes was 3.

[0065] (3) The alcohol gel was placed in a mixed solution containing trimethylchlorosilane and n-hexane for solvent replacement and surface modification, wherein the volume ratio of trimethylchlorosilane to n-hexane was 1:20, the required temperature was 55℃, and the required time was 24h.

[0066] (4) The modified wet gel was placed in a drying oven and dried at normal pressure at a temperature of 80°C for 5 hours.

[0067] The aerogel prepared in Example 2 was subjected to adsorption-desorption tests under the following conditions: degassing temperature of 150°C and degassing time of 7 hours. The adsorption-desorption isotherm is shown below. Figure 2 As shown, from Figure 2 As can be seen, it conforms to a type IV isotherm with an H3-type hysteresis loop, indicating that there are a large number of mesopores in the aerogel.

[0068] The specific surface area, average pore size, and pore volume of the aerogels prepared in Examples 1-4 and Comparative Example 1 were tested, and the results are shown in Table 1:

[0069] Table 1

[0070] Example 1 589 20.1 2.8 Example 2 618 19.2 2.9 Example 3 562 21.2 2.4 Example 4 599 19.8 3.1 Comparative Example 1 602 19.7 2.9

[0071] As can be seen from the data in Table 1, the silica aerogel obtained by the preparation method of this invention is almost identical to the aerogel obtained by existing technologies in terms of specific surface area, average pore size, and pore volume, indicating that this preparation method is feasible. Compared with existing technologies, the method of this invention is cheaper, simpler, and faster, providing a new technical route for the large-scale preparation of low-cost silica aerogels.

[0072] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0073] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a silica aerogel material, characterized in that, Includes the following steps: (1) Add water glass to sulfuric acid, and after it forms a gel, put it in water for aging to obtain a wet gel; the aging temperature is 40~65℃ and the aging time is 2~5h. (2) The wet gel obtained in step (1) is placed in a modification solution and modified under heating conditions. The modification solution consists of a solvent and a modifier. The solvent is hexamethyldisiloxane, the modifier is trimethylchlorosilane, and the volume ratio of the solvent to the modifier is (20~100):

1. The temperature of the modification treatment is 105~130℃, and the heating rate is 2.5~5℃ / min. The liquid evaporated during the modification treatment is condensed and recovered. The volume ratio of the solvent to the wet gel is (3~6):

1. (3) The modified wet gel is dried to obtain silica aerogel material.

2. The method for preparing silica aerogel material according to claim 1, characterized in that, In step (1), the concentration of sulfuric acid is 1.8~3 mol / L; the volume ratio of water glass to sulfuric acid is (3.8~4.3):

1.

3. In the method for preparing silica aerogel material according to claim 1, the modification treatment time in step (2) is 8~12h.

4. The method for preparing silica aerogel material according to claim 1, characterized in that, In step (3), the drying temperature is 110~120℃ and the drying time is 2~6h.

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