Preparation process of aerogel

Abstract

The invention discloses a preparation process of aerogel. The preparation process comprises the following specific steps: putting wet gel into a soaking solution for soaking and aging; wherein before the wet gel is put in, ammonia gas is introduced into the soak solution; the introduction amount of the ammonia gas is 0.2%-0.9% by taking the mass of the soaking solution as a calculation reference. Ammonia gas adopted by the method is better controlled compared with stronger ammonia water, and the addition amount of stronger ammonia water in actual production is unstable due to the fact that the volatility of stronger ammonia water in a traditional process is easily influenced by temperature fluctuation; the ammonia gas can be accurately regulated and controlled through a flow meter, so that the consistency of process parameters is ensured; moreover, only the moisture content of the ammonia gas needs to be controlled, so that real-time adjustment through rectification operation is facilitated, multivariable interference is avoided, and the method has a very good practical value in industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of aerogel preparation, and in particular to a process for preparing aerogel. Background Art

[0002] In the process of preparing aerogel products in the prior art, there is an important process step of soaking and aging before drying. Its main purpose is to make the polycondensation reaction more complete, further cross-link the colloidal particles inside the gel, and enhance the stability of the network structure. At the same time, this process can also optimize the pore structure of the gel to form a more uniform pore size distribution; make the gel network more stable, and reduce the stress caused by solvent evaporation in the subsequent drying process; during the aging process, water, some impurities or unreacted substances produced by polycondensation will precipitate from the gel.

[0003] Since alkali is often used as a catalyst in the gel process, it has a great influence on the gel time and the degree of polycondensation. In order to control the gel time in the production process, the amount of alkaline substances is usually appropriately reduced in the gel process to improve the operability of production. Therefore, in the process of soaking and aging, the existing technology often adopts the method of adding a part of alkali to the system to ensure the thoroughness of the gel reaction and the quality of the gel.

[0004] At present, the most commonly used alkali in the soaking aging process in the industry is ammonia water. However, since the ammonia water added during aging contains a considerable amount of water, it is necessary to replace this part of the water with anhydrous alcohol solvents to reduce the moisture content in the product. At the same time, this step also produces the replaced, water-containing alcohol solvent, which needs to be distilled to remove the water in it so that the alcohol solvent can be reused. This not only increases the processing cost, but also reduces the quality of the product after aging. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a process for preparing aerogel to solve the problems in the prior art of difficulty in handling the aqueous methanol produced after alcohol replacement of the water in the product after immersion aging and reduced product performance.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation process of aerogel, the specific steps are as follows:

[0008] The wet gel is placed in a soaking liquid for soaking aging; wherein, before the wet gel is placed in the soaking liquid, ammonia is introduced into the soaking liquid; the amount of ammonia introduced is 0.2% to 0.9% based on the mass of the soaking liquid.

[0009] Preferably, the immersion aging temperature is 40° C. to 60° C., and the immersion aging time does not exceed 14 hours.

[0010] Preferably, the wet gel is prepared by the following steps:

[0011] A silicon source, a catalyst and an alcohol solvent are mixed to prepare a silica sol, and then the silica sol is gelled under the catalytic action of the catalyst to obtain a wet gel.

[0012] Preferably, when preparing silica sol, the molar ratio of the silicon source, the catalyst and the alcohol solvent is (1-1.5): (4-6): (10-15).

[0013] Preferably, during gelation, the mass ratio of silica sol to catalyst is (6-15):(1-2).

[0014] Preferably, the silicon source includes one or more of methyl orthosilicate, ethyl orthosilicate, methyltrimethoxysilane, and methyltriethoxysilane.

[0015] Preferably, the catalyst is an acidic or alkaline catalyst; wherein the acidic catalyst includes one or more of hydrochloric acid, oxalic acid, citric acid, nitric acid, and acetic acid; the alkaline catalyst is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

[0016] Preferably, the alcohol solvent is one or more of methanol, ethanol and propanol.

[0017] Preferably, the aged wet gel is dried to obtain an aerogel material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. In the present invention, during the soaking aging process, a proper amount of ammonia is first introduced into the soaking liquid before the wet gel is placed therein for aging, which brings about unexpected technical effects: after replacing ammonia water with ammonia gas, the product quality and performance are significantly improved, and the thermal conductivity is significantly reduced. This is because after a proper amount of ammonia is dissolved in the soaking liquid, it can adjust the charge distribution on the gel surface, inhibit the capillary action during the drying process, and reduce the collapse of the pore structure, thereby forming a more uniform microporous network, and ultimately the product has a better thermal conductivity; at the same time, a proper amount of ammonia can inhibit the volatility of the residual organic solvent, so that the VOC content in the product is controllable, thereby further reducing the difficulty of subsequent processing.

[0020] 2. The present invention uses ammonia gas instead of ammonia water. Compared with the traditional process using ammonia water, the traditional process uses concentrated ammonia water and is easy to volatilize. The quality of concentrated ammonia water will be affected by the environment and fluctuate significantly. This often requires adjustment when adding ammonia water to the production system, increasing the operation steps and production costs. The present invention completely omits this step and also reduces the water content in the soaking liquid, which can accelerate the gel aging reaction rate. Taking a 35-ton soaking liquid system as an example, only introducing ammonia gas accounting for 0.7% of the mass of the soaking liquid can reduce the introduction of 810kg of water, and the aging time can be shortened to one-third of the original aging time, reducing the distillation energy consumption and the difficulty of wastewater treatment.

[0021] 3. In the traditional process, the moisture brought in by ammonia water often needs to be removed by distillation, which will produce a considerable amount of high-boiling point organic wastewater and even high-boiling substances. These high-boiling substances need to be treated as hazardous waste, which increases the production cost. After the present invention uses ammonia gas instead of ammonia water, not only the amount of high-boiling point organic wastewater is significantly reduced, the amount of high-boiling substances is also reduced a lot, and at the same time, the number of distillation times is also significantly reduced, and the overall production cost is further reduced.

[0022] 4. The ammonia gas used in the present invention is also easier to control than concentrated ammonia water. In the traditional process, concentrated ammonia water is easily affected by temperature fluctuations due to its volatility, resulting in unstable addition amount during actual production; while ammonia gas can be precisely controlled by a flow meter to ensure the consistency of process parameters; and ammonia gas only needs to control its water content, which is convenient for real-time adjustment through distillation operation to avoid multivariate interference, and has good practical value in industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of immersion aging in the present invention. DETAILED DESCRIPTION

[0024] The present invention will be combined with the drawings in 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, not all of 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.

[0025] 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.

[0026] 1. A preparation process of aerogel, the specific steps are as follows:

[0027] The wet gel is placed in a soaking liquid for soaking aging; wherein, before the wet gel is placed in the soaking liquid, ammonia is introduced into the soaking liquid; the amount of ammonia introduced is 0.2% to 0.9% based on the mass of the soaking liquid.

[0028] After studying the existing process, the present invention found that in order to control the gel time in the production process, the amount of alkaline substances is usually appropriately reduced in the gel process to improve the operability of production. Therefore, in the soaking and aging process, after adding ammonia water to the soaking liquid, a large amount of water will be introduced into the system. During the same soaking and aging time, the quality of the product is relatively poor, resulting in a significant increase in the time and energy consumption of the subsequent drying process; in addition, the replacement frequency of the soaking liquid system increases, resulting in an increase in the consumption of alcohol solvents used for replacement. Moreover, the difficulty of handling methanol after replacement is also significantly increased, which is mainly reflected in the distillation process of the alcohol solvent after replacement. Not only is the number of distillations of the alcohol solvent more, but also the output of water-containing high-boiling substances is significantly increased. This high-boiling substance is identified as a hazardous solid waste and requires special treatment, and its disposal cost is significantly increased.

[0029] In view of these phenomena, the present invention has conducted an in-depth investigation and found that it is due to the added ammonia water: ① The addition of ammonia water introduces a large amount of water into the system, and water is a by-product of the polycondensation reaction. The increase in its content will inhibit the efficiency of the polycondensation reaction, resulting in a decrease in the aging rate and an extension of the aging time; ② The addition of additional water interferes with the original water replacement function of the alcohol solvent, reduces its replacement efficiency for the water inside the gel, and requires multiple and large-scale alcohol liquid replacement to control the water content in the product within the required range; ③ The increase in the water content of the system requires frequent alcohol solvent replacement, which not only increases the solvent consumption, but also leads to a large amount of alcohol solvent replaced with water, which often requires multiple distillations to be processed to be qualified. At the same time, more high-boiling substances are produced during the distillation process, and the difficulty of processing is further increased.

[0030] In the process of exploring solutions, the present invention unexpectedly discovered that replacing ammonia water with ammonia gas not only solves the problem of excessive water introduction into the system, but also has unexpected technical effects: after replacing ammonia water with ammonia gas, the product quality and performance are significantly improved, and the thermal conductivity is significantly reduced. This is because after a proper amount of ammonia gas is dissolved in the soaking liquid, it can adjust the charge distribution on the gel surface, inhibit the capillary action during the drying process, and reduce the collapse of the pore structure, thereby forming a more uniform microporous network, and ultimately making the product have a better thermal conductivity; at the same time, a proper amount of ammonia gas can inhibit the volatility of residual organic solvents, making the VOC content in the product controllable, thereby further reducing the difficulty of subsequent processing; traditional processes generally use concentrated ammonia water and are easy to volatilize. The quality of concentrated ammonia water will be affected by the environment and fluctuate significantly, which often requires adjustment when adding ammonia water to the production system. Increase the operation steps and production costs; the present invention completely omits this step, and also reduces the water content in the soaking liquid, which can accelerate the gel aging reaction rate. Taking a 35-ton soaking liquid system as an example, only introducing ammonia gas accounting for 0.7% of the mass of the soaking liquid can reduce the introduction of 810kg of water, and the aging time can be shortened to one third of the original aging time, reducing the distillation energy consumption and the difficulty of wastewater treatment; in the traditional process, the water introduced by ammonia water often needs to be removed by distillation, which will produce a considerable amount of high-boiling point organic wastewater and even high-boiling substances. These high-boiling substances need to be treated as hazardous waste, which increases the production cost; after the present invention uses ammonia gas instead of ammonia water, not only the amount of high-boiling point organic wastewater is significantly reduced, the amount of high-boiling substances is also reduced a lot, and at the same time, the number of distillation times is also very significantly reduced, and the overall production cost is further reduced.

[0031] In some embodiments of the present invention, the present invention uses ammonia gas instead of ammonia water, which can promote faster aging. In the past, it was necessary to soak for more than 14 hours to make the product have a good thermal conductivity. In the present invention, the soaking time can be further shortened; in the present invention, the effect of aging after 5 hours after the introduction of ammonia gas can reach the effect of 7 hours after the addition of ammonia water, or even better. Therefore, in the present invention, the soaking aging temperature can be further reduced, which can be 40°C, 45°C, 50°C, 55°C or 60°C, or in the numerical range consisting of any two of the above specific values ​​as endpoints; the soaking aging time does not exceed 14 hours. Although the thermal conductivity of the product will further decrease after 14 hours, the decline is significantly slowed down. Therefore, the soaking aging time is further preferably 5h to 14h, which can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h or 14h, or in the numerical range consisting of any two of the above specific values ​​as endpoints. It should be understood that in the implementation plan, any of the above ranges can be combined with any other ranges.

[0032] In some embodiments of the present invention, the present invention does not specifically limit the type and preparation method of the wet gel. The present invention is applicable to various wet gels, and is particularly applicable to systems using alkaline catalysts. The wet gel is prepared by the following steps: a silicon source, a catalyst, and an alcohol solvent are mixed to form a silica sol, and then the silica sol is gelled under the catalytic action of the catalyst to obtain a wet gel.

[0033] In some embodiments of the present invention, when preparing silica sol, the molar ratio of the silicon source, the catalyst and the alcohol solvent is (1-1.5): (4-6): (10-15). The molar ratio of the silicon source, the catalyst and the alcohol solvent can be 1:4:10, 1:4:15, 1:6:10, 1:6:15, 1.5:4:10, 1.5:6:15 or 1.2:5:12, or in a numerical range consisting of any two of the above specific values ​​as endpoints. It should be understood that in the embodiments, any of the above ranges can be combined with any other ranges.

[0034] In some embodiments of the present invention, during gelation, the mass ratio of silica sol to catalyst is (6-15):(1-2). The mass ratio of silica sol to catalyst can be 6:1, 6:2, 15:1, 15:2 or 10:1.5, or a numerical range consisting of any two of the above specific values ​​as endpoints. It should be understood that in the embodiments, any of the above ranges can be combined with any other ranges.

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

[0036] In some embodiments of the present invention, the catalyst is an acidic or alkaline catalyst; wherein the acidic catalyst includes one or more of hydrochloric acid, oxalic acid, citric acid, nitric acid, and acetic acid; the alkaline catalyst is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

[0037] In some embodiments of the present invention, the alcohol solvent is one or more of methanol, ethanol, and propanol.

[0038] In some embodiments of the present invention, the aged wet gel is dried to obtain an aerogel material.

[0039] II. Specific Implementation

[0040] The specific process is as follows Figure 1 As shown, wet gels with completely the same components and contents were prepared using the prior art as samples, and then the experiments of the embodiments and comparative examples were carried out respectively.

[0041] Example 1

[0042] Step 1: In a 100L soaking tank, the mass of the soaking liquid is used as the base for calculation, and the ammonia gas flow rate is controlled to be 0.2%.

[0043] Step 2: Soak the wet gel sample in the soaking solution treated in step 1 at 50° C. for 8 hours, and then perform supercritical drying to obtain the product.

[0044] Example 2

[0045] The method is improved on the basis of Example 1, except that the amount of ammonia introduced is 0.3%. The other steps are exactly the same as those of Example 1.

[0046] Example 3

[0047] The method is improved on the basis of Example 1, except that the amount of ammonia introduced is 0.5%. The other steps are exactly the same as those of Example 1.

[0048] Example 4

[0049] The method is improved on the basis of Example 1, except that the amount of ammonia introduced is 0.7%. The other steps are exactly the same as those of Example 1.

[0050] Example 5

[0051] The method is improved on the basis of Example 1, except that the amount of ammonia introduced is 0.9%. The other steps are exactly the same as those of Example 1.

[0052] Comparative Example 1

[0053] The improvement is made on the basis of Example 1, and the difference is that: the amount of ammonia water added is 0.3% calculated based on the mass of the soaking liquid. In the soaking system of this comparative example 1, the amount of ammonia added is the same as that in Example 4. The other steps are exactly the same as those in Example 1.

[0054] Comparative Example 2

[0055] The method is improved on the basis of Example 1, and the difference therefrom is that ammonia gas is not introduced, and step 2 is directly performed. The other steps are exactly the same as those of Example 1.

[0056] Comparative Example 3

[0057] The method is improved on the basis of Example 1, except that the amount of ammonia introduced is 0.1%. The other steps are exactly the same as those of Example 1.

[0058] Comparative Example 4

[0059] The method is improved on the basis of Example 1, except that the amount of ammonia introduced is 1.0%. The other steps are exactly the same as those of Example 1.

[0060] Comparative Example 5

[0061] The method is improved on the basis of Example 1, except that the amount of ammonia introduced is 1.2%. The other steps are exactly the same as those of Example 1.

[0062] 3. Performance Comparison

[0063] The thermal conductivity and VOC content of the products prepared in the examples and comparative examples were measured. At the same time, attention was paid to the treatment of the alcohol solvents in the examples and comparative examples after replacement with the same anhydrous alcohol solvent.

[0064] Table 1

[0065]

[0066] It can be seen from the embodiments and comparative examples that:

[0067] (1) The introduction of an appropriate amount of ammonia can significantly improve product quality. The introduction of ammonia can adjust the charge distribution on the gel surface, inhibit the capillary action during the drying process, and reduce the collapse of the pore structure, thereby forming a more uniform microporous network, and ultimately making the product have a better thermal conductivity. At the same time, an appropriate amount of ammonia can inhibit the volatility of residual organic solvents, making the VOC content in the product controllable. However, excessive introduction of ammonia will cause the gel to gel too quickly, the micropores to become larger, and the thermal conductivity of the product to increase. It will also make the VOC content in the product too high and difficult to meet the requirements.

[0068] (2) The wastewater of the embodiment and the comparative example were statistically analyzed. Since ammonia gas was directly introduced, the moisture content in the soaking system was significantly reduced. Calculated based on 35 tons of soaking liquid, the amount of ammonia gas added was 0.7%. Compared with the addition of an equal amount of ammonia water in the traditional process, 810 kg of water introduction can be reduced at one time. Overall, the number of distillation drainage times in the embodiment was significantly lower than that in the comparative example 1, and the distillation energy consumption and the amount of high-boiling products produced showed a very significant decrease.

[0069] (3) The present invention is applied to actual production. Under the premise of ensuring that the soaking system contains an equal amount of ammonia, the amount of ammonia gas added is compared with that of ammonia water added per 100m 3 The former produces 1 t less high-boiling substances than the latter, and the former performs two-thirds less distillation on the replaced alcohol solvent than the latter, saving 2500Kw / h in overall energy consumption.

[0070] Then, taking Example 4 and Comparative Example 1 as examples, the two were subjected to different immersion aging time treatments, and the thermal conductivity coefficients of the products were compared, as shown in Table 2.

[0071] Table 2

[0072]

[0073] From Table 2 we can see that:

[0074] (1) Under the same aging time, the introduction of ammonia gas can make the thermal conductivity of the product better than that of ammonia water; this shows that the introduction of ammonia gas significantly reduces the introduction of water into the immersion system, and the reduction of water in the immersion system can accelerate the efficiency of the forward reaction of gel aging, making the product age faster and improving production efficiency.

[0075] (2) In order to achieve similar thermal conductivity, Example 4 obviously requires a shorter time, while Comparative Example 1 requires a longer time. Taking the thermal conductivity of about 0.015 W / (m·K) as an example, Example 4 only requires 12 h, while Comparative Example 1 exceeds 14 h. However, from Example 4, when the amount of ammonia introduced remains unchanged, the longer the aging time, the smaller the contribution to the thermal conductivity. For the improved method of introducing ammonia, too long aging time does not bring more positive feedback. Therefore, the aging time does not need to be too long when introducing ammonia.

[0076] 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 process for preparing aerogel, characterized in that: The specific steps are as follows: The wet gel is placed in a soaking liquid for soaking aging; wherein, before the wet gel is placed in the soaking liquid, ammonia is introduced into the soaking liquid; the amount of ammonia introduced is 0.2% to 0.9% based on the mass of the soaking liquid.

2. The preparation process according to claim 1, characterized in that: The immersion aging temperature is 40℃~60℃, and the immersion aging time does not exceed 14h.

3. The preparation process according to claim 1, characterized in that: The wet gel is prepared by the following steps: A silicon source, a catalyst and an alcohol solvent are mixed to prepare a silica sol, and then the silica sol is gelled under the catalytic action of the catalyst to obtain a wet gel.

4. The preparation process according to claim 3, characterized in that: When preparing silica sol, the molar ratio of silicon source, catalyst and alcohol solvent is (1-1.5): (4-6): (10-15).

5. The preparation process according to claim 2, characterized in that: During gelation, the mass ratio of silica sol to catalyst is (6-15):(1-2).

6. The preparation process according to claim 3, characterized in that: The silicon source includes one or more of methyl orthosilicate, ethyl orthosilicate, methyltrimethoxysilane and methyltriethoxysilane.

7. The preparation process according to claim 3, characterized in that: The catalyst is an acidic or alkaline catalyst; wherein the acidic catalyst includes one or more of hydrochloric acid, oxalic acid, citric acid, nitric acid, and acetic acid; the alkaline catalyst is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

8. The preparation process according to claim 3, characterized in that: The alcohol solvent is one or more of methanol, ethanol and propanol.

9. The preparation process according to claim 3, characterized in that: The aged wet gel is dried to obtain an aerogel material.

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