A solvent replacement method accelerated by microwave irradiation and a method for preparing aerogel

Abstract

The present invention discloses a method for solvent replacement accelerated by microwave irradiation and a method for preparing aerogel. A non-polar solvent is used to replace the solvent in the wet gel, and microwave irradiation heating is adopted during the replacement process; the surface tension of the non-polar solvent is not greater than 18 dyn / cm, the molecular polarity is less than 15, and it is not flammable. By reasonably selecting an organic solvent with non-polarity and extremely low surface tension, without adding other polar substances, only relying on a small amount of microwave irradiation, the energy of the microwave can be accurately applied to the water and methanol (or ethanol) molecules that need to be replaced inside the gel. Through the high-speed movement of these molecules, they escape from the inside of the gel and the vacancies are filled by the non-polar solvent with low surface tension, thus achieving a rapid "extraction" effect of the solvent molecules, which is beneficial to improving the replacement efficiency and ensuring production safety.

Description

Technical Field

[0001] The present invention relates to the technical field of gel materials, and in particular to a solvent replacement method accelerated by microwave irradiation and a method for preparing aerogel. Background Art

[0002] In the atmospheric drying process of aerogel, in order to reduce the damage of the capillary force during drying to the skeleton structure, it is necessary to use a low surface tension solvent to replace the water and other reactants in the wet gel, and this process is called solvent replacement. In the traditional aerogel preparation process, usually several times or even dozens of times the volume of the wet gel of the solvent is used for replacement, and multiple replacements are required. In addition, in order to minimize the capillary force caused by the surface tension of the solvent during drying as much as possible, usually after replacing the solvent with ethanol or methanol, it is also necessary to use a low surface tension solvent such as n-hexane for secondary solvent replacement.

[0003] Therefore, this process requires a large amount of time (about 2-4 days), and consumes a large amount of solvent, resulting in a significant increase in the preparation time and cost of aerogel. The main reason for this problem is that the solvent replacement process only relies on the molecular diffusion caused by the concentration gradient between different solvents to achieve solvent replacement, which is a very low-efficiency replacement method, not only slow in speed but also difficult to achieve complete replacement.

[0004] For this reason, some studies have tried to improve the replacement speed by heating, stirring and other methods, but the effects are not satisfactory. For example, the invention patent CN102557052A adsorbs water / alcohol in the solvent by adding a desiccant in the solvent to ensure the concentration gradient of water molecule diffusion, so as to strengthen the solvent replacement, but it is easy to introduce impurities and even block the internal pore diameter.

[0005] Microwave irradiation is a commonly used method in chemical processes, and is mostly used in the heating process. This method has been applied in small amounts in the preparation process of aerogel. For example, the invention patents CN107082431A and CN107246783A both adopt the method of using microwave to accelerate the drying of aerogel. The invention patent CN101633505A uses microwave irradiation to accelerate the hydrolysis and polycondensation reaction of the sol-gel process. The invention patent CN109529735A discloses a microwave integrated machine for producing aerogel materials and a method for continuously producing aerogel materials. This method uses microwave technology to accelerate the preparation process in all stages of gel generation, solvent replacement and drying.

[0006] However, in the existing microwave irradiation solvent replacement methods, the whole solvent is mostly heated by using polar molecules or polar substances, which is also the most common application of microwave technology. For example, in the invention patent CN109529735A, a microwave absorber is added to the gel to absorb microwave energy, and then the energy is transferred to the solvent molecules. In fact, it accelerates the solvent replacement by means of enhanced heating. In this application method, the microwave will heat the whole gel and solvent, which is likely to cause a rapid increase in the solvent temperature and lead to explosion, and the energy consumption is relatively high. In addition, most of the organic solvents used in traditional solvent replacement methods are flammable, such as methanol, ethanol, isopropanol, n-pentane, n-hexane, etc. These solvents are very likely to cause accidents such as combustion and explosion under microwave conditions. Therefore, except for small-scale laboratory use, the microwave irradiation accelerated replacement technology is basically not applied in the industrial production of aerogels. Summary of the Invention

[0007] The technical problem to be solved by the present invention is as follows: For solvent replacement based on concentration gradient, it takes a long time and consumes a large amount of solvent; for acceleration of replacement by heating, such as in the microwave heating process, explosion is extremely likely to occur, which is not conducive to large-scale industrial production. The present invention provides a method for preparing aerogel accelerated by microwave irradiation to solve the above problems.

[0008] The present invention is realized by the following technical solutions:

[0009] A method for accelerating solvent replacement by microwave irradiation, which uses a non-polar solvent to replace the solvent in the wet gel, and microwave irradiation heating is adopted during the replacement process; the surface tension of the non-polar solvent is not greater than 18 dyn / cm and the molecular polarity is less than 15.

[0010] For the above technical problems, the conventional approach is to improve the gel preparation process, heating process, selection of polar replacement solvents, and subsequent drying process, etc. The present invention analyzes and studies and finds that the organic solvents such as water, methanol, ethanol, and isopropanol involved in the wet gel are all polar solvents. For example, the polarity of water is 80.4 and that of ethanol is 24.3, which have very good conditions for applying microwave irradiation technology. Therefore, by reasonably selecting non-polar and organic solvents with extremely low surface tension, without adding other polar substances, only relying on a small amount of microwave irradiation, the energy of the microwave can be accurately applied to the water and methanol (or ethanol) molecules that need to be replaced inside the gel. Through the high-speed movement of these molecules, they escape from the inside of the gel, and the vacancies are filled by non-polar solvents with low surface tension, thus achieving a rapid "extraction" effect of solvent molecules, which is conducive to improving the replacement efficiency and ensuring production safety.

[0011] The amount of the non-polar solvent should be greater than 2 times the volume of the wet gel, and it is ensured that the wet gel is always immersed in the non-polar solvent during the replacement process.

[0012] More preferably, the non-polar solvent is insoluble or slightly soluble in water.

[0013] More preferably, the non-polar solvent includes fluorinated organic solvents, which can be used alone or as a mixed solvent mainly composed of fluorinated organic solvents. Among them, fluorinated organic solvents include but are not limited to 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,3,3-pentafluorobutane (HFC-365mfc), methyl nonafluorobutyl ether (methoxy nonafluorobutane), 1,1,1,2,2,3,4,5,5,5-decafluoropentane (HFC-4310mee), etc., and can be a combination of one or two or more of the above non-polar solvents.

[0014] More preferably, when replacing the solvent in the wet gel with a non-polar solvent, the non-polar solvent is replaced at intervals, and the purity of the non-polar solvent replaced later is equal to or greater than the purity of the non-polar solvent replaced earlier. It is preferred that the purity of the non-polar solvent replaced later is greater than the purity of the non-polar solvent replaced earlier; if the purity of the non-polar solvents replaced before and after is very high, they can be designed to have equal purity.

[0015] As the solvent replacement progresses, polar organic solvents such as water, methanol, or ethanol in the wet gel will be discharged from the inside, reducing the purity of the non-polar solvent and the replacement efficiency. Therefore, it is necessary to replace the replacement solvent (i.e., the non-polar solvent) or rectify it for recycling to ensure the replacement speed and effect.

[0016] More preferably, the non-polar solvent is replaced every 5 min to 30 min, and the total number of replacements is not less than 2 times; the purity of the non-polar solvent before the first replacement is not less than 80%, and the purity of the non-polar solvent after the last replacement is not less than 95%.

[0017] More preferably, during the microwave irradiation heating process, the power of the microwave irradiation is set to reach the set temperature for the non-polar solvent within 1 min to 5 min, and the set temperature is 0 to 15 °C lower than the boiling point of the non-polar solvent; the microwave irradiation time is 10 min to 120 min.

[0018] The power of the microwave irradiation is determined according to the volume of the aerogel; the irradiation time is preferably 20 min to 60 min.

[0019] More preferably, the wet gel includes silica wet gel, organic-inorganic hybrid silica wet gel, and silica-based functional materials.

[0020] Further preferably, the raw materials for preparing the silica wet gel include: a silicon source, a catalyst, and an auxiliary agent; a siloxane monomer or polysiloxane with one or more methyl groups is used alone as the silicon source; or a siloxane monomer or polysiloxane with one or more methyl groups and a tetraalkyl orthosilicate are used together as the silicon source.

[0021] The silica wet gel is obtained by reacting the above raw materials through hydrolysis and polycondensation processes. Among them, the siloxane monomers include, but are not limited to, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, etc.; the polysiloxanes include, but are not limited to, polyvinylpolydimethylmethoxysilane, polyvinylpolymethyldimethoxysilane, etc.; the catalysts include, but are not limited to, acidic catalysts and basic catalysts; other auxiliary agents include, but are not limited to, drying control agents, pore-forming agents, etc.

[0022] Further preferably, a structural support material is also included; the structural support material includes, but is not limited to, inorganic fibers, organic fibers, porous materials, cloth, net, film, etc.

[0023] A method for preparing an aerogel uses the above-mentioned microwave irradiation-accelerated solvent replacement method to replace the solvent in the wet gel; then, through drying treatment, a gel product is obtained.

[0024] Further preferably, the drying treatment process sequentially includes pre-drying, low-temperature drying, and high-temperature drying; the pre-drying is carried out in an environment filled with a non-polar solvent, the drying temperature is 25°C to 70°C, and the drying time is 1h to 12h; the low-temperature drying is carried out in an air, inert gas protection, negative pressure, or vacuum environment, the drying temperature is 25°C to 80°C, and the drying time is 1h to 24h; the high-temperature drying is carried out in an air, inert gas protection, negative pressure, or vacuum environment, the drying temperature is 120°C to 250°C, and the drying time is 60min to 240min.

[0025] The pre-drying temperature is preferably the boiling point of the non-polar solvent, and the drying time is preferably 4h to 6h. At the beginning of drying, the replacement container is filled with the saturated vapor of the non-polar solvent. During the pre-drying process, by controlling the evaporation rate of the non-polar solvent, the vapor pressure of the non-polar solvent in the drying container is slowly reduced from the saturated state, thereby reducing the shrinkage and collapse of the pores of the wet gel caused by the rapid evaporation of the solvent.

[0026] The pre-drying, low-temperature drying, and high-temperature drying can be heated by methods including, but not limited to, infrared heating, far-infrared heating, or hot air circulation, etc. The non-polar solvent vapor generated by drying can be recovered through a condensing device.

[0027] Since the non-polar solvent is immiscible with water and the density of water is generally less than that of the non-polar solvent, the water displaced by the solvent can be discharged in advance through a water separator, reducing the energy consumption of the subsequent non-polar solvent rectification.

[0028] The present invention has the following advantages and beneficial effects:

[0029] 1. By utilizing the difference in molecular polarity between the solvent to be replaced and the replacement solvent, and adopting microwave irradiation to heat polar molecules, the polar molecules inside the wet gel are actively moved out, thus rapidly achieving solvent replacement. The solvent replacement time, which originally took 1 to 2 days, is shortened to 0.5 h to 2 h, greatly shortening the solvent replacement time, enhancing the solvent replacement effect, and significantly reducing the solvent consumption. In this process, the highly polar solvent is located in the internal voids of the wet gel, while the non-polar replacement solvent is located outside the wet gel. Under the action of microwaves, the highly polar water and solvent molecules inside the wet gel, after being affected by microwaves, move much faster than the low-polarity (or non-polar) solvent molecules outside, and the heating rate is much faster than that of the non-polar organic solvent outside. Therefore, they will accelerate their movement towards the outside of the wet gel, and the voids left by them will gradually be filled by the non-polar organic solvent outside, thereby achieving rapid solvent replacement. The replacement speed of the solvent under the action of microwaves is much higher than that of the traditional method relying solely on diffusion replacement by concentration difference. The traditional solvent replacement method relies on the diffusion action of molecular concentration difference. Therefore, there are a large number of water and solvent molecules in the wet gel that cannot be replaced due to small pores, surface adsorption, etc. Microwave irradiation can directly act on these molecules, enabling them to have enough energy to break free from the bondage and move to the outside of the wet gel, enhancing the solvent replacement effect. In addition, since it does not rely on diffusion replacement by concentration difference, the consumption of the replacement solvent can also be significantly reduced, only one-tenth to one-fifth of the original solvent consumption.

[0030] 2. The present invention uses non-flammable or less flammable organic solvents to replace the flammable organic solvents such as ethanol, methanol, isopropanol, and n-hexane often used in the traditional solvent replacement method. Due to the existence of these flammable organic solvents, when applying microwave technology, it is very easy to cause fire or explosion due to reasons such as electric sparks and overheating, presenting a very large potential safety hazard. Using less flammable organic solvents well solves this problem. Even if the replaced solvents such as methanol and ethanol are volatilized by heat during the microwave irradiation process, their proportion in the vapor generally does not exceed the explosion limit value.

[0031] 3. The present invention utilizes non-polar organic solvents that are immiscible with water, making the separation of the replaced water and the solvent very simple. Most of the replaced water can be rapidly separated through a water separator, thereby reducing the energy consumption of solvent distillation and the discharge of waste liquid.

[0032] 4. The present invention realizes the cascaded utilization of the replacement solvent, significantly reducing the amount of the replacement solvent used. At different stages of replacement, different purity requirements are imposed on the replacement solvent. In the early stage of replacement, the requirement for the solvent purity is relatively low, while in the later stage of replacement, a higher purity is required. When it is necessary to batch-prepare aerogels, taking advantage of this feature, only newly or rectified and recycled high-purity replacement solvents are used in the later stage of replacement, while used replacement solvents with relatively low purity are used in the early stage of replacement, and these used and low-purity replacement solvents are only rectified and recycled or discarded. This significantly reduces the use of the replacement solvent and also reduces the energy consumption for solvent rectification and recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0034] Figure 1 is the working flow chart of the present invention;

[0035] Figure 2 is the schematic structural diagram of the adaptation of the replacement container and the microwave device of the present invention;

[0036] Figure 3 is the schematic structural diagram of the drying container of the present invention; wherein Figure A shows the side cross-sectional structural diagram, and Figure B shows the top view;

[0037] Figure 4 is the schematic overall structural diagram of the aerogel preparation equipment of the present invention.

[0038] Reference numerals in the drawings and corresponding component names: 1 - replacement container, 2 - porous partition I, 3 - upper cover plate, 4 - temperature sensor, 5 - microwave device, 6 - reflux device, 7 - pipeline, 8 - separator, 21 - microporous cover plate, 22 - drying container, 23 - porous partition II, 24 - through hole, 9 - non-polar solvent, 10 - sol, 11 - low-temperature drying oven, 12 - high-temperature drying oven, 13 - condenser. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and do not limit the present invention.

[0040] Embodiment 1

[0041] This embodiment provides a method for preparing aerogels accelerated by microwave irradiation, and the specific steps are as follows:

[0042] Step 1, solvent replacement:

[0043] Put the prepared wet gel A into a 1L glass container, add the non-polar solvent DuPont Vertrel XF (perfluoropentane) with a purity of 99% until the container is almost full, cover the upper cover on the wet gel A, and at the same time ensure that the wet gel is immersed below the liquid level of the non-polar solvent. Put the glass container into a microwave reactor and carry out microwave heating. Set the microwave heating time to 15 min, the microwave power to 500 W, and the microwave heating temperature to 45 °C; replace the fresh Vertrel XF (perfluoropentane) every 15 min and continue microwave heating for 15 min, and replace it twice. The obtained gel is named wet gel B. After the used perfluoropentane separates the displaced water through a water separator, it is uniformly collected and rectified and recycled using a rectification column.

[0044] Step 2, pre-drying:

[0045] Place the wet gel B in a glass box, and use a pipette to drip 20 ml of perfluoropentane on the surface of the wet gel B. Place the glass box in a drying oven and dry it at 45 °C for 2 h for pre-drying. The pre-dried wet gel is named wet gel C.

[0046] Step 3, low-temperature drying:

[0047] Dry the wet gel C at 60 °C for 12 h for low-temperature drying to obtain a semi-dried aerogel D.

[0048] Step 4, high-temperature drying:

[0049] Take out the glass box, put the low-temperature dried aerogel D on a stainless steel tray, and dry it in a drying oven at 150 °C for 30 min for high-temperature drying to obtain a completely dried aerogel E. The prepared aerogel is in block shape, with a thermal conductivity of 0.0162 W / (m·K) and a density of 0.013 g / cm 3 .

[0050] Note: (1) The above mass parts can be mg, g or kg, and in this embodiment, it refers to "g".

[0051] (2) For the wet gel A, in this embodiment, the following wet gel is taken as an example: Under the condition of a 40 °C water bath, add 55.3 mass parts of methyltrimethoxysilane, 6.4 mass parts of cetyltrimethylammonium bromide, 83.2 mass parts of acetic acid with a concentration of 0.01 mol / L, 5.8 mass parts of urea, and 166.5 mass parts of methanol to a 500 mL volumetric flask in sequence, stir evenly for 30 min to form a transparent sol, pour it into a mold, seal it, and then put the mold into a drying oven at 70 °C and age it for 24 h. The obtained wet gel is named wet gel A.

[0052] Example 2

[0053] All raw materials and processes are the same as those in Example 1, but the time for each microwave replacement is set to 30 min. The prepared aerogel is in a block shape, with a thermal conductivity of 0.0160 W / (m·K) and a density of 0.013 g / cm 3 .

[0054] Example 3

[0055] All raw materials and processes are the same as those in Example 1, but the non-polar solvent used is changed to Enasolv 365F (the main component is 1,1,1,3,3-pentafluorobutane), and the microwave heating temperature is set to 40 °C. The prepared aerogel is in a block shape, with a thermal conductivity of 0.0165 W / (m·K) and a density of 0.014 g / cm 3 .

[0056] Example 4

[0057] All raw materials and processes are the same as those in Example 1, but the silicon source used is changed to a mixture of 41.47 parts by mass of methyltrimethoxysilane and 13.83 parts by mass of methyl silicate. The prepared aerogel is in a block shape, with a thermal conductivity of 0.0171 W / (m·K) and a density of 0.015 g / cm 3 .

[0058] Example 5

[0059] All raw materials and processes are the same as those in Example 1, but the silicon source used is changed to a mixture of 36.87 parts by mass of methyltrimethoxysilane and 18.43 parts by mass of polysiloxane. The prepared aerogel is in a block shape, with a thermal conductivity of 0.0192 W / (m·K) and a density of 0.018 g / cm 3 .

[0060] Example 6

[0061] A transparent sol is prepared using the same raw materials as in Example 1. A non-woven fabric with a side length of 10 cm and a thickness of 0.2 mm is fully impregnated in the sol and then placed in a mold. The subsequent processes are the same as those in Example 1. An aerogel heat-insulating cloth is prepared.

[0062] Example 7

[0063] 1 part by mass of chopped glass fibers with a diameter of 3 μm to 10 μm and a length of 2 mm to 10 mm is dispersed in 2 parts by mass of ethanol in a high-speed disperser for 15 min. A transparent sol is prepared using the same raw materials as in Example 1. 2 parts by mass of the transparent sol is added to the dispersion and stirred evenly, then poured into a mold and flattened into a film with a thickness of 0.8 mm. The subsequent processes are the same as those in Example 1. An aerogel heat-insulating and flame-retardant film is prepared.

[0064] Comparative Example 1

[0065] All raw materials and processes are the same as those in Example 1, except that: methanol (a polar solvent) is used as the replacement solvent. Before replacement, the air in the replacement container needs to be evacuated, and the grounding of the microwave device and the ventilation nearby should be done well to prevent explosion. The prepared aerogel is in a fragmented shape, with a thermal conductivity of 0.0203 W / (m·K) and a density of 0.016 g / cm 3 。

[0066] Comparative Example 2

[0067] All raw materials and processes are the same as those in Example 1, except that: the heating method, heating temperature and time during the replacement process are different. The replacement container is directly placed in an oven, the heating temperature is set at 60 °C, and the heating time is 24 h. The prepared aerogel is in a fragmented shape, with a thermal conductivity of 0.022 W / (m·K) and a density of 0.020 g / cm 3 。

[0068] Testing method:

[0069] (1) Testing method for thermal conductivity: The thermal conductivity is measured using an Xiangtan Xiangyi DRPL-III thermal conductivity tester (plate heat flux meter method). Before testing, the sample to be measured is ground into powder with a particle size of about 30 μm to 100 μm.

[0070] (2) Testing method for density: The density is measured using a Shunyu Hengping electronic density balance AE124J.

[0071] Table 1 Performance parameters of the aerogel products obtained in Examples 1 - 5

[0072] Sample Thermal conductivity W / (m·K)) <![CDATA[Density (g / cm 3 )]]> Example 1 0.0162 0.013 Example 2 0.0160 0.013 Example 3 0.0165 0.014 Example 4 0.0171 0.015 Example 5 0.0192 0.018 Comparative Example 1 0.0203 0.016 Comparative Example 2 0.0220 0.020

[0073] In summary, the present invention provides a method for accelerating solvent replacement by microwave irradiation and a method for preparing aerogel. This method makes full use of the differences in polarity and surface tension between solvent molecules during solvent replacement. By using the microwave irradiation method, the highly polar and high surface tension water and methanol (or ethanol) inside the aerogel are replaced with non-polar and low surface tension fluorinated organic solvents, significantly shortening the solvent replacement time, greatly improving the solvent replacement effect, and significantly reducing the solvent consumed in the replacement.

[0074] Example 8

[0075] This embodiment provides a gel solvent replacement device for implementing the replacement method in the above embodiments (such as any one of Embodiment 1, or Embodiments 2-7), including a replacement container 1 and a microwave device 5. The replacement container 1 is used to hold the replacement solvent and the wet gel; the microwave device 5 surrounds the replacement container 1 and is used to emit microwaves to heat the replacement solvent and the wet gel in the replacement container 1. The replacement container 1 is placed inside the microwave device 5, designed such that the microwave device 5 surrounds the replacement container 1; or multiple microwave devices are uniformly arranged around the replacement container 1, designed such that the microwave device 5 surrounds the replacement container 1, for heating the replacement solvent and the wet gel in the replacement container 1. This embodiment uses a closable microwave device 5 to directly place the replacement container 1 inside the microwave device 5 for heating.

[0076] The replacement container 1 includes a container body, an upper cover plate 3, and a porous partition I 2; the container body is used to hold the replacement solvent and the wet gel, the upper cover plate 3 covers the top opening of the container body, and the porous partition I 2 is used to be arranged above the wet gel to restrict the upward movement of the wet gel due to buoyancy. The upper cover plate 3 covers the top opening of the container body to form a sealed replacement container 1; the peripheral circumferential side wall of the porous partition I 2 is axially connected to the inner wall of the middle part of the container body, dividing the container body into upper and lower layers. The porous partition I 2 can be set in the middle of the container body by its own gravity, or fixed by detachable connectors (such as bolts, buckles, etc.).

[0077] Three through holes are provided on the upper cover plate 3, which are respectively used to install a temperature sensor 4, one pipeline 7 as an output pipeline, and another pipeline 7 as an input pipeline. The temperature sensor 4 is used to detect the temperature of the solvent in the replacement container 1. The inlet end of the output pipeline is communicated with the inside of the replacement container 1 and is used to discharge the used replacement solvent in the replacement container 1; the outlet end of the input pipeline is communicated with the inside of the replacement container 1 and is used to input new replacement solvent into the replacement container 1. It also includes a separator 8 and a reflux device 6; the input end of the separator 8 is connected to the outlet end of the output pipeline and is used to separate the water displaced from the replacement solvent and the wet gel; the output end of the reflux device 6 is connected to the inlet end of the input pipeline and is used to input the condensed replacement solvent or new replacement solvent into the replacement container 1 through the input pipeline.

[0078] Further, this embodiment provides a device for implementing the preparation of aerogel in the above embodiment, including the above gel solvent replacement device, and further including a drying container 22, a microporous cover plate 21, and a porous partition II 23. A porous partition II 23 is installed in the drying container 22, and the wet gel after solvent replacement to be dried is placed on the porous partition II 23. The top open end of the drying container 22 is covered with the microporous cover plate 21, and a plurality of through holes 24 are provided on the microporous cover plate 21 for the circulation of gas or vapor. The microporous cover plate 21 is detachably arranged on the upper port of the drying container 22. A number of micropores with a diameter of 0.5 mm to 1.5 mm are opened on the microporous dry plate 21, and the number of micropores is determined according to the volume of the drying container 22, with an average of 0.5 to 6 micropores per liter. The microporous cover plate 21 is removed during the high-temperature drying process.

[0079] It further includes a low-temperature drying oven 11 and a high-temperature drying oven 12. Herein, the "low temperature" and "high temperature" refer to the relative operating temperatures of the low-temperature drying oven 11 and the high-temperature drying oven 12, which are relative to each other and related to the boiling point of the replacement solvent, rather than the drying temperature that the drying equipment itself can reach. The actual operating temperature of the low-temperature drying oven 11 is lower than the operating temperature of the high-temperature drying oven 12. The drying container 22 is placed in the low-temperature drying oven 11, and the high-temperature drying oven 12 is used to dry the gel dried in the low-temperature drying oven 11.

[0080] It further includes a condenser 13, and the exhaust hole of the low-temperature drying oven 11 or the exhaust hole of the high-temperature drying oven 12 is connected to the condenser 13. The exhaust holes of both the low-temperature drying oven 11 and the high-temperature drying oven 12 are connected to the condenser 13, and are connected to the same condenser 13 or respectively connected to different condensers 13.

[0081] The process of preparing aerogel using the aerogel preparation device provided in Embodiment 8 is as follows:

[0082] Step 1, place the pre-prepared silica wet gel in the replacement container 1, add a non-polar solvent as the replacement solvent (such as one or more of 1,1,1,3,3-pentafluoropropane, 1,1,1,3,3-pentafluorobutane, methyl nonafluorobutyl ether, 1,1,1,2,2,3,4,5,5,5-decafluoropentane) in the replacement container 1, submerge the silica wet gel in the non-polar solvent, and cover the wet gel with a porous partition I above to prevent the wet gel from floating due to the buoyancy of the non-polar solvent.

[0083] Step 2, place the replacement container 1 in the microwave device 5, turn on the microwave device, and heat the non-polar solvent and the wet gel in the replacement container 1.

[0084] Step 3, pre-drying: Place the wet gel processed in Step 2 in a microporous drying container filled with non-polar solvent vapor for pre-drying.

[0085] Step 4, low-temperature drying: subject the wet gel pre-dried in Step 3 to low-temperature drying; both pre-drying and low-temperature drying are performed by placing the drying container 11 in the low-temperature drying oven 11.

[0086] Step 5, high-temperature drying: the high-temperature drying process can be directly performed by placing the wet gel on a stainless steel tray and putting it in the drying oven 12.

[0087] Pre-drying, low-temperature drying, and high-temperature drying can be heated by means including but not limited to infrared heating, far-infrared heating, or hot air circulation. The non-polar solvent vapor generated during drying needs to be recovered through the condenser 13.

[0088] When replacing the operation by inputting a new replacement solvent into the replacement container 1 through the input pipeline, or by inputting the separated and processed replacement solvent into the replacement container 1 through the input pipeline and the reflux device 6, it is cycled or replaced every 5 - 30 minutes, and the number of cycles or replacements is not less than 2 times. The purity of the non-polar solvent is not less than 80% before the first replacement, and not less than 95% after the last replacement.

[0089] The above specific embodiments further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A solvent replacement method accelerated by microwave irradiation, characterized in that, A non-polar solvent is used to displace the solvent in the wet gel, and microwave irradiation heating is used during the displacement process; The surface tension of the non-polar solvent is not greater than 18 dyn / cm, and the molecular polarity is less than 15; The non-polar solvent includes a fluorinated organic solvent.

2. The solvent replacement method accelerated by microwave irradiation according to claim 1, wherein The non-polar solvent is insoluble or slightly soluble in water.

3. A solvent replacement method accelerated by microwave irradiation according to claim 1, characterized in that, When using a non-polar solvent to displace the solvent in the wet gel, the non-polar solvent is replaced at intervals, and the purity of the non-polar solvent replaced later is equal to or greater than the purity of the non-polar solvent replaced earlier.

4. A solvent replacement method accelerated by microwave irradiation according to claim 3, characterized in that, The non-polar solvent is replaced every 5 min to 30 min, and the total number of replacements is not less than 2 times; the purity of the non-polar solvent before the first replacement is not less than 80%, and the purity of the non-polar solvent after the last replacement is not less than 95%.

5. A solvent replacement method accelerated by microwave irradiation according to claim 1, characterized in that, During the microwave irradiation heating process, the power of the microwave irradiation is set to reach the set temperature for the non-polar solvent within 1 min to 5 min, and the set temperature is 0 to 15 °C lower than the boiling point of the non-polar solvent; the microwave irradiation time is 10 min to 120 min.

6. The solvent replacement method accelerated by microwave irradiation according to claim 1, wherein The wet gel includes a silica wet gel and an organic-inorganic hybrid silica wet gel.

7. A solvent replacement method accelerated by microwave irradiation according to claim 1, characterized in that, The wet gel includes a silica-based functional material.

8. A solvent replacement method accelerated by microwave irradiation according to claim 6, characterized in that The raw materials for preparing the silica wet gel include: a silicon source, a catalyst, and an auxiliary agent; a siloxane monomer or polysiloxane with one or more methyl groups is used alone as the silicon source; or a siloxane monomer or polysiloxane with one or more methyl groups and a tetraalkyl orthosilicate are used together as the silicon source.

9. A solvent replacement method accelerated by microwave irradiation according to claim 8, characterized in that, It also includes a structural support material; the structural support material includes inorganic fibers, organic fibers, porous materials, cloth, net, and film.

10. A method for preparing aerogel, characterized in that, Using the solvent displacement method accelerated by microwave irradiation according to any one of claims 1 to 9, displace the solvent in the wet gel; then through a drying process to obtain a gel product.

11. A method for preparing aerogel according to claim 10, characterized in that, The drying process sequentially includes pre-drying, low-temperature drying, and high-temperature drying; The pre-drying is carried out in an environment filled with a non-polar solvent, the drying temperature is 25 °C to 70 °C, and the drying time is 1 h to 12 h; For the low-temperature drying, the drying temperature is 25 °C to 80 °C, and the drying time is 1 h to 24 h; For the high-temperature drying, the drying temperature is 120 °C to 250 °C, and the drying time is 60 min to 240 min.

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