Silica aerogel based on microchannel technology and its preparation method and device

Abstract

The application provides a silica aerogel based on a microchannel technology and a preparation method and device thereof; the preparation method comprises continuously inputting raw materials into a microchannel mixing reaction device, continuously carrying out sol-gel conversion, solvent replacement and hydrophobic modification, and then drying to obtain silica aerogel and continuously outputting. By using the technical scheme of the application, the high specific surface area of the microchannel can be used to realize the rapid mixing of reactants to form microgel; the high mass transfer efficiency of the microchannel can greatly shorten the solvent replacement and hydrophobic modification time and save a large amount of solvent; compared with a traditional intermittent preparation method of silica aerogel, the method integrates the preparation process into a single microchannel system, solves the problems of multi-step dispersion and discontinuity, and each link is independent, detachable and combinable, and is flexible and efficient.

Description

Technical Field

[0001] This invention relates to the field of nanoporous materials technology, specifically to a method for preparing nanoporous aerogel materials, and more specifically, to a silica aerogel based on microchannel technology, its preparation method, and apparatus. Background Technology

[0002] Aerogels were first proposed in 1931 by S.S. Kistler of Stanford University, who introduced the concept of replacing the liquid phase in a gel with a gas phase and invented silica aerogel. However, due to the high technical barriers in aerogel preparation, its development stagnated for about thirty years. It wasn't until 1966 that J.B. Riel used alkoxysilanes instead of sodium silicate in Kistler's work, preparing silica aerogels via a one-step sol-gel method using silica esters, which rapidly advanced research in the field. Based on their skeletal composition, aerogels are classified into three categories: inorganic aerogels (including silica aerogels and metal oxide aerogels), organic aerogels (often with resorcinol-formaldehyde as a precursor), and carbon aerogels. Silica aerogel is the most representative of these. The pore size of silica aerogel nanoporous structures ranges from 5 to 150 nm, with an average pore size of 20 to 40 nm. They are characterized by low density, high porosity, high specific surface area, and low thermal conductivity, and have broad application prospects in fields such as thermal insulation, catalyst support, and optics (Nature, 1931, 127(3211): 741-741; The Journal of Physical Chemistry, 1966, 70(9): 2937-2945).

[0003] The preparation process of aerogel includes: (1) Sol-gelation. This is the core process for preparing aerogel. Under the action of a catalyst, the precursor is hydrolyzed and condensed to form a gel. Adjusting the reaction conditions can control the microstructure of the gel skeleton; (2) Aging. This is the process of dissolving and re-condensing the uneven gel particles, which enhances the connection between secondary particles and obtains larger aggregated particles, thereby enhancing the aerogel skeleton; (3) Solvent replacement. In preparation for the subsequent drying process, a large amount of solvent with low surface tension is used to replace the water in the gel, which can obtain nanoparticles with better dispersibility.

[0004] Taking silica as an example, current methods for preparing silica aerogels include one-step and two-step methods (Particle & Particle Systems Characterization, 2023: 2200186). The one-step method involves mixing a molecular precursor, water, solvent, and a catalyst (acid or base), placing the mixture in a container, and allowing it to stand for a certain period to allow the gel to slowly form. The size of the nanostructured units is controlled by adding surfactants. However, precursors such as TMOS and TEOS require a large amount of solvent to dilute the silica sol, limiting aerogel formation in the one-step method. Therefore, the two-step method was proposed as a solution. In the first stage of the two-step method, the precursor undergoes hydrolysis and condensation using an acid catalyst; then, it is dissolved in a non-alcoholic solution such as acetone to complete the hydrolysis and fixation, forming a silica aerogel. The two-step method allows for highly controllable pore structures in silica aerogels and avoids the technical problems caused by solvent dilution in the one-step method, making it the preferred technique for preparing standard aerogel structures.

[0005] However, in existing technologies, the conventional two-step method for preparing aerogels is typically an intermittent process. This process suffers from discontinuity, lack of integration, and large aerogel sizes, which severely limits the mass and heat transfer properties of the aerogels. Furthermore, the solvent replacement step involves a large amount of solvent, resulting in waste. Similarly, the preparation of silica aerogels in existing technologies suffers from the same problems: discontinuity and multi-step dispersion complicate the process, requiring significant manpower, material resources, and effort, leading to low production efficiency and high production costs. In particular, the large aerogel size causes instability in mass and heat transfer, resulting in time-consuming stirring of the reaction products, slow or even incomplete solvent replacement, problems that are urgently needed.

[0006] On the other hand, microchemical technology is a multidisciplinary, cutting-edge scientific field that emerged in the early 1990s. In the past decade or so, research and applications of microchemical technologies, such as micromixing and multiphase microflow, microheat and mass transfer, and microscale reactions, have been conducted both domestically and internationally, ushering in a new era of efficient and refined chemical engineering. The core of microchemical technology is the microchannel reactor, which uses microstructural units as its core. By reducing the dispersion scale of the system, it enhances mixing and transport, improves process controllability and efficiency, and scales up micro-devices based on the principle of "scale-up," directly applying laboratory results to industrial processes to achieve large-scale production. Research on microchemical technology aims to enhance the safety of chemical processes, promote process intensification and miniaturization of chemical systems, and improve energy and resource utilization efficiency, with broad application prospects. Among these, microfluidics, as one of the core technologies of microchemical engineering, can precisely manipulate and process micro-volume multiphase flows in microchannels, providing the possibility for achieving efficient and controllable microchemical processes. The application of microfluidics has expanded from early uses in analytical chemistry and inkjet printing to cutting-edge emerging fields such as the synthesis of fine chemicals and new materials, high-throughput analysis, and the simulation of cells and intracellular systems.

[0007] Chinese invention patent CN108975342A discloses a method for continuously preparing silica aerogel spheres using a vibrating hydrophobic surface. The method involves pumping a mixed solution through a syringe and dripping it onto a vibrating hydrophobic shaker to form a gel. The wet silica gel is then transferred, aged, solvent-displaced, hydrophobically modified, and dried to obtain silica aerogel spheres. This method aims to solve problems such as low efficiency, inability to produce continuously, and decreased quality in the preparation of SiO2 aerogel spheres. However, although this preparation method uses a syringe, it is not related to microchannel technology. It first mixes and reacts the reactants, then uses vibration to induce a gel transformation, which is completely different from this invention patent. Chinese invention patent CN105289431B discloses a method for preparing porous NIPAAm aerogel microcapsules, which includes using a transparent solution containing NIPAAm monomer as the dispersed phase and an oily substance mixture as the continuous phase. The two are injected into a T-shaped microchannel at a certain mass ratio using a syringe to obtain a mixed liquid containing microcapsules. After standing, washing, and freeze-drying, porous NIPAAm aerogel microcapsules are obtained. This method prepares gel droplets in the microchannel and performs gel separation and collection at the microchannel outlet. Chinese invention patent CN109650396A discloses a method for preparing silica aerogel. The method involves reacting silica with sodium hydroxide using ethanol / water as a solvent to generate modified sodium silicate. An inorganic acid is then added to the modified sodium silicate solution to generate a modified silica sol, removing inorganic salt byproducts. The modified silica sol is then subjected to a specific temperature and pressure to generate a modified silica gel. The modified silica gel is then subjected to solvent exchange with a non-polar solvent and dried to obtain a hydrophobic aerogel material. This method is a traditional batch preparation process, with each preparation step performed independently, and is not a continuous process.

[0008] Based on this, the present invention provides a method for preparing silica aerogel using microchemical technology. Utilizing the safety of microreactors, it allows for rapid mixing of reactants, providing uniform reaction concentration, uniform reaction time, uniform temperature, and rapid heat exchange, without scale-up effects. This method promises to achieve continuous, integrated, and efficient silica aerogel preparation. Compared to existing technologies, the present invention eliminates the need to introduce an oil phase into the microchannels, thus eliminating the need for subsequent rinsing and removal processes. The reactants undergo a sol-gel reaction within the microchannels, completing the liquid-solid transition and ensuring full utilization of the reactants. The macroscopic size of the resulting aerogel is related to the inner diameter of the microchannels. Therefore, the present invention provides a novel method for dynamic solvent replacement within microchannels. Summary of the Invention

[0009] This invention discloses a silica aerogel based on microchannel technology and its preparation method and apparatus, in order to overcome the shortcomings of the prior art.

[0010] To achieve the above objectives, the present invention provides a continuous preparation method for silica aerogel based on microchannel technology, comprising continuously feeding raw materials into a microchannel mixing reaction device, continuously performing sol-gel transformation and solvent replacement, drying to generate silica aerogel, and continuously outputting the aerogel.

[0011] Preferably, the microchannel mixing reaction device includes at least a continuous sol-gel transition section and a first solvent replacement section; the continuous sol-gel transition section is a T-shaped microchannel, including multiple input ends arranged in parallel, a T-shaped micromixer for mixing reaction raw materials, and a microchannel I connected to the T-shaped micromixer; the length of the microchannel I is 10cm to 100cm; the inner diameter of the microchannel I is 0.1mm to 1mm; the first solvent replacement section includes a microchannel II; the microchannel II is a microtube wrapped with a PTFE microfiltration membrane; the pore size of the micropores in the microfiltration membrane is 0.22μm to 5μm; the inner diameter of the microtube is the same as the inner diameter of the microchannel I; the length of the microchannel II is 5cm to 100cm.

[0012] Preferably, after the reaction raw materials are input to the input end, they enter the microchannel I for continuous sol-gel reaction to obtain sol-gel products; the sol-gel products enter the microchannel II, and at the same time, a replacement solvent is injected into the first solvent replacement chamber to perform solvent replacement and obtain wet gel.

[0013] Preferably, the organosiloxane precursor solution and the alkaline catalyst are pumped into microchannel I through different input terminals, with a total pumping flow rate of 0.1 mL / min to 20 mL / min. This can be understood as the rate at which the liquid is pumped into the microchannel being the flow rate for the reaction to occur within the microchannel.

[0014] Preferably, the sol-gel reaction conditions include a reaction temperature of 20°C to 60°C.

[0015] Preferably, the organosiloxane precursor solution comprises an organosiloxane monomer and an organic solvent.

[0016] Preferably, the silicon content in the organosiloxane precursor solution is 2wt% to 20wt%.

[0017] Preferably, the organosiloxane monomer comprises any one or a combination of two or more of tetraethyl orthosilicate, tetramethyl orthosilicate, methyltrimethoxysilane, and dimethyldimethoxysiloxane.

[0018] Preferably, the alkaline catalyst includes either ammonia or sodium hydroxide solution; the solvent of the alkaline catalyst includes either ethanol or water; and the concentration of the alkali in the alkaline catalyst is 1 mol / L to 15 mol / L.

[0019] Preferably, the organic solvent includes any one or a combination of two or more of methanol, ethanol, dimethylformamide, dimethyl sulfoxide, and water.

[0020] Preferably, the replacement solvent is selected from any one or a combination of two or more of methanol, ethanol, tert-butanol, n-hexane, n-heptane, and cyclohexane.

[0021] Preferably, the volumetric flow rate of the displacement solvent input or output is 0.1 mL / min to 200 mL / min.

[0022] Preferably, the microchannel mixing reaction device further includes a modification section, which includes microchannel III and a modification chamber, microchannel IV and a second solvent replacement chamber; microchannel III is placed inside the modification chamber and connected to the first solvent replacement chamber;

[0023] The microchannel IV is placed inside the second solvent replacement chamber and connected to the modification chamber.

[0024] Preferably, a modifier is introduced into the modification cavity, and after the wet gel enters the microchannel III, surface modification is performed; then, it continues to enter the microchannel IV, and the solvent replacement operation is repeated to obtain the modified wet gel.

[0025] Preferably, microchannel III and microchannel IV are extensions of microchannel II, and microchannel III and microchannel IV have the same inner diameter as microchannel II; the length of microchannel III or microchannel IV is 5cm to 100cm.

[0026] Preferably, the volumetric flow rate of the displacement solvent and / or the modifier input or output is 0.1 mL / min to 200 mL / min.

[0027] Preferably, the replacement solvent is selected from any one or a combination of two or more of methanol, ethanol, tert-butanol, n-hexane, n-heptane, and cyclohexane.

[0028] Preferably, the modifier is a hydrophobic modifier selected from any one or a combination of two or more of trimethylchlorosilane, hexamethyldisilazane, and hexamethyldisiloxane.

[0029] Preferably, the replacement solvent is input to or output to the first solvent replacement chamber and / or the second solvent replacement chamber in a dynamic input-output manner.

[0030] Preferably, the modifier is input into or output from the modification cavity in a dynamic manner.

[0031] Preferably, the drying process includes supercritical drying, freeze drying, atmospheric pressure drying, and / or airflow spray drying.

[0032] Specifically, the supercritical drying includes: replacing the liquid components inside the gel material with a supercritical fluid in a supercritical state to obtain an aerogel material, wherein the supercritical fluid used includes any one of supercritical CO2, supercritical methanol, and supercritical ethanol.

[0033] Preferably, the freeze-drying includes vacuum freeze-drying under reduced pressure; the vacuum freeze-drying includes freezing the gel material below the freezing point and then sublimating the solvent under a higher vacuum to obtain an aerogel material; preferably, the freezing method includes: pre-freezing in a freezing device and freezing directly in a drying chamber by rapid vacuuming; more preferably, the cold trap temperature of the vacuum freeze-drying is -45°C to -80°C, and the vacuum degree is less than 0.1 kPa.

[0034] Preferably, the atmospheric pressure drying includes: replacing the pore solution in the wet gel with one or more solvents with low surface tension, and evaporating the solvent at atmospheric pressure to obtain an aerogel material; more preferably, the evaporation temperature is 20°C to 200°C.

[0035] Preferably, the airflow spray drying includes evaporating and drying the gel material after thoroughly mixing it with natural air; the temperature of the natural air is 20°C to 200°C.

[0036] The silica aerogel prepared by the above method has a density of 0.04 g / cm³. 3 ~0.3g / cm 3 Its size ranges from 0.1mm to 1mm, and its specific surface area is 500m². 2 / g~1200m 2 / g, with a thermal conductivity of 0.015W / mk to 0.045W / mk.

[0037] As one of the objectives of this invention, this invention also provides the above-mentioned microchannel mixing reaction apparatus for preparing silica aerogel, which includes at least a continuous sol-gel transition section and a first solvent replacement section. The continuous sol-gel transition section is a T-shaped microchannel, including multiple input ends arranged in parallel, a T-shaped micromixer for mixing reaction raw materials, and a microchannel I connected to the T-shaped micromixer. The first solvent replacement section includes a microchannel II and a first solvent replacement chamber connected in parallel, and the microchannel II is disposed in the first solvent replacement chamber.

[0038] Preferably, the microchannel I is a PTFE capillary; the microchannel I is 10cm to 100cm long; and the inner diameter of the microchannel I is 0.1mm to 1mm.

[0039] The microchannel II is a microtube wrapped with a PTFE microfiltration membrane; the micropores contained in the microfiltration membrane have a pore size of 0.22μm to 5μm; the inner diameter of the microtube is the same as the inner diameter of the microchannel I; the length of the microchannel II is 5cm to 100cm.

[0040] In one preferred embodiment, the microchannel mixing reaction device further includes a modification section and a second solvent replacement section; the modification section and the second solvent replacement section can be multiple repeating units to modify the surface of the wet gel material; the modification section includes microchannel III and a modification cavity, microchannel IV and a second solvent replacement cavity; microchannel III is placed in the modification cavity and connected to the first solvent replacement cavity; microchannel IV is placed in the second solvent replacement cavity and connected to the modification cavity.

[0041] Preferably, microchannel III and microchannel IV are extensions of microchannel II; the length of microchannel III or microchannel IV is 5cm to 100cm.

[0042] Compared with the prior art, the advantages of the present invention are as follows:

[0043] 1. The method for preparing silica aerogel based on a microchannel mixing reaction device provided by the technical solution of the present invention utilizes the extremely high specific surface area of ​​the microchannel to achieve rapid mixing of reactants to form microgels; the high mass transfer efficiency of the microchannel can greatly shorten the solvent replacement and hydrophobic modification time and save a large amount of solvent; compared with the traditional batch preparation method of aerogel, this method integrates the preparation process into a single microchannel system, solving the problems of multi-step dispersion and discontinuity, and each step is independent, separable and combinable, which is flexible and efficient.

[0044] 2. The technical solution of this invention, based on a microchannel mixing reaction device, has the characteristics of small scale-up effect, simple reaction system, and is easy to produce continuously on a large scale.

[0045] 3. The technical solution of this invention can fully leverage the advantages of rapid mixing, high mass transfer efficiency, and highly integrated preparation process of microchannels, enabling the preparation of silica aerogels to be completed within one day, greatly shortening the preparation cycle of aerogels, while saving a large amount of solvent, improving production efficiency and reducing production costs.

[0046] 5. The method for continuous preparation of silica aerogel based on microchannels provided by this invention enables continuous operation of continuous feeding, continuous reaction, and continuous discharge through microchannels, thereby improving production efficiency and realizing the continuous, integrated, and efficient preparation process of silica aerogel.

[0047] 5. The technical solution of this invention has the advantages of simple preparation process, mild and controllable reaction conditions, low energy consumption, green and pollution-free nature, suitability for large-scale production, and broad application prospects. Attached Figure Description

[0048] Figure 1 This is a flowchart illustrating the continuous preparation of silica aerogels based on a microchannel mixing reaction device according to the present invention.

[0049] Figure 2 This is a sample image of the hydrophilic silica aerogel prepared in Example 1 of the present invention.

[0050] Figure 3 This is a scanning electron microscope image of the hydrophilic silica aerogel prepared in Example 1 of the present invention.

[0051] Figure 4 This is an optical microscope image of the hydrophilic silica aerogel prepared in Example 1 of the present invention.

[0052] Figure 5 This is a scanning electron microscope image of the hydrophilic silica aerogel prepared in Example 2 of the present invention.

[0053] Figure 6 This is an optical microscope image of the hydrophilic silica aerogel prepared in Example 2 of the present invention.

[0054] Figure 7 This is a scanning electron microscope image of the hydrophobic silica aerogel prepared in Example 6 of the present invention.

[0055] Figure 8 This is a nitrogen adsorption curve of the hydrophobic silica aerogel prepared in Example 6 of the present invention.

[0056] Figure 9 This is a pore size distribution diagram of the hydrophobic silica aerogel prepared in Example 6 of the present invention.

[0057] Figure 10 The image shows the TG curve of the hydrophobic silica aerogel prepared in Example 6 of this invention.

[0058] Figure 11 The contact angle diagram is shown for the hydrophobic silica aerogel prepared in Example 6 of this invention.

[0059] Figure 12 The contact angle diagram is shown for the hydrophobic silica aerogel prepared in Example 7 of this invention.

[0060] Figure 13 The infrared spectra of the hydrophilic silica aerogels prepared in Example 1 and Comparative Example 1 of this invention are shown.

[0061] Figure 14 This is a contact angle diagram of the hydrophobic silica aerogel prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0063] This invention provides a method for continuously preparing silica aerogel based on microchannels, comprising: continuously inputting a precursor solution, an alkaline catalyst, a solvent, and a modifier for preparing the silica aerogel into a T-shaped microchannel, continuously performing sol-gel transition, solvent replacement, and hydrophobic modification, and continuously outputting the silica aerogel generated in the microchannel; then drying to obtain silica aerogel, and continuously outputting it.

[0064] Furthermore, methods for the continuous preparation of silica aerogels based on microchannels include:

[0065] (1) The organosiloxane precursor solution and alkaline catalyst were pumped into the T-type microchannel at a certain volume flow rate and a certain reaction temperature to carry out continuous sol-gel transformation.

[0066] (2) The obtained wet gel is further fed into the solvent replacement microchannel II, and at the same time, the replacement solvent is input into the replacement chamber I at a certain volume flow rate. The solvent is dynamically introduced and removed.

[0067] Steps (3) and (4), which can be performed or not performed, include:

[0068] (3) The obtained wet gel is further fed into the hydrophobic modified microchannel III, and at the same time, the modifier is introduced into the replacement chamber II at a certain volume flow rate. The modifier is introduced and discharged in a dynamic manner.

[0069] (4) The obtained wet gel is fed into the solvent replacement microchannel IV, while the solvent is fed into the replacement chamber III at a certain volume flow rate. The solvent is fed in and out in a dynamic manner.

[0070] (5) The obtained wet gel is dried by a special drying method to obtain silica aerogel.

[0071] In some embodiments, the organosiloxane precursor solution comprises an organosiloxane monomer and a solvent.

[0072] Further, the organosiloxane monomer includes any one or a combination of two or more of tetraethyl orthosilicate, tetramethyl orthosilicate, methyltrimethoxysilane, and dimethyldimethoxysiloxane; the solvent includes any one or a combination of two or more of methanol, ethanol, dimethylformamide, dimethyl sulfoxide, and water; and the silicon content in the organosiloxane precursor solution is 2 wt% to 20 wt%.

[0073] In some embodiments, the alkali in the alkaline catalyst includes either ammonia or sodium hydroxide, the solvent of the alkaline catalyst includes either ethanol or water, and the concentration of the alkali in the alkaline catalyst is 1 mol / L to 15 mol / L.

[0074] In some embodiments, the total volumetric flow rate of the organosiloxane precursor solution and the alkaline catalyst is pumped into the microchannel device at a rate of 0.1 mL / min to 20 mL / min.

[0075] In some embodiments, the sol-gel reaction temperature is 20°C to 60°C.

[0076] In some embodiments, the replacement solvent is selected from any one or a combination of two or more of methanol, ethanol, tert-butanol, n-hexane, n-heptane, and cyclohexane.

[0077] In some embodiments, the modifier is selected from any one or a combination of two or more of trimethylchlorosilane, hexamethyldisilazane, and hexamethyldisiloxane.

[0078] In some embodiments, the microchannel I is selected as a PTFE capillary; the microchannel I is 10cm to 100cm long; and the inner diameter of the microchannel I is 0.1mm to 1mm.

[0079] In some embodiments, the microchannel II is a microtube wrapped with a PTFE microfiltration membrane; the micropores contained in the microfiltration membrane have a pore size of 0.22μm to 5μm; the inner diameter of the microtube is the same as the inner diameter of the microchannel I; and the length of the microchannel II is 5cm to 100cm.

[0080] In some embodiments, microchannel III or microchannel IV is an extension of microchannel II; the length of microchannel III or microchannel IV is 5cm to 100cm.

[0081] In some embodiments, the volumetric flow rate of the displacement solvent and / or the modifier input or output is 0.1 mL / min to 200 mL / min.

[0082] In some embodiments, the special drying method includes supercritical drying, freeze drying, atmospheric pressure drying, and airflow spray drying; and / or the supercritical drying technology is characterized by using a supercritical fluid to replace the liquid component inside the gel material in a supercritical state to obtain an aerogel material, wherein the supercritical fluid used includes, but is not limited to, any one of supercritical CO2, supercritical methanol, and supercritical ethanol; and / or the freeze drying technology includes vacuum freeze drying and reduced pressure drying, characterized by freezing the gel material below the freezing point and then sublimating the solvent under a higher vacuum to obtain the aerogel material; and / or the freezing method includes: pre-freezing in a freezing device and direct freezing in a drying chamber by rapid vacuuming. Vacuum freeze-drying has a cold trap temperature of -45℃ to -80℃ and a vacuum degree of less than 0.1 kPa; and / or atmospheric pressure drying technology is characterized by replacing the pore solution in the wet gel with one or more solvents with low surface tension, and evaporating the solvent at atmospheric pressure and a certain temperature (20℃ to 200℃) to obtain an aerogel material; and / or, airflow spray drying technology is characterized by thoroughly mixing the gel material with heated natural air (20℃ to 200℃), achieving evaporation and drying in a short time due to the large heat and mass exchange area. Atmospheric pressure drying technology and airflow spray drying technology are particularly preferred.

[0083] In some embodiments, the density of the silica aerogel is 0.04 g / cm³. 3 ~0.3g / cm 3 Its size ranges from 0.1mm to 1mm, and its specific surface area is 500m². 2 / g~1200m 2 / g, with a thermal conductivity of 0.015W / mk to 0.045W / mk.

[0084] The method for continuous microchannel preparation of silica aerogel based on the above technical solution enables continuous industrial production of silica aerogel. The raw materials and aerogel products continuously enter and exit the microchannel, and the microchannel facilitates rapid mixing and high mass transfer efficiency. This method can solve the problems of long preparation cycles and large amounts of wasted solvent in existing silica aerogel production.

[0085] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0086] Example 1

[0087] This invention is based on a method for continuously preparing silica aerogel using a microchannel mixing reaction device.

[0088] Among them, see Figure 1The microchannel mixing reaction device includes at least a T-type micromixer, microchannel I, solvent replacement microchannel II, and solvent replacement chamber arranged in sequence. The raw materials for the reaction are pumped into the T-type microchannel through several injection units for mixing and continuous sol-gel transformation.

[0089] After continuing into microchannel I to achieve continuous sol-gel transition, it enters solvent replacement microchannel II, where the first solvent replacement is performed in the first solvent replacement chamber to obtain silica wet gel, which is then dried to obtain hydrophilic silica aerogel.

[0090] Alternatively, the wet gel obtained after the first solvent exchange enters the modification chamber through microchannel II, where it undergoes modification under the action of a modifier to obtain a modified wet gel. It then enters the second solvent exchange chamber through microchannel III for a second solvent exchange to obtain a modified wet gel. Finally, after drying, a hydrophobic silica aerogel is obtained.

[0091] The first solvent replacement chamber, the modification chamber, and the second solvent replacement chamber include solvent inlets and outlets, enabling them to achieve a dynamic working mode of the solvent during operation.

[0092] Specifically, microchannel I is made of PTFE capillary; the length of microchannel I is 10cm to 100cm; the inner diameter of microchannel I is 0.1mm to 1mm.

[0093] Specifically, microchannel II is a microtube wrapped with a PTFE microfiltration membrane; the micropores contained in the microfiltration membrane have a diameter of 0.22μm to 5μm; the inner diameter of the microtube is the same as that of microchannel I; and the length of microchannel II is 5cm to 100cm.

[0094] Specifically, microchannel III or microchannel IV is an extension of microchannel II; the length of microchannel III or microchannel IV is 5cm to 100cm.

[0095] The method for preparing silica aerogel based on the above-mentioned microchannel mixing reaction device includes the following specific steps:

[0096] 1. Preparation of organosiloxane precursor solution: 15g TEOS was polycondensed in 13.3g ethanol and 2.5g water to form organosiloxane precursor solution. The silicon content in the organosiloxane was 6.6wt%.

[0097] 2. Preparation of catalyst: A certain amount of ammonia water is added to ethanol and stirred to form an alkaline catalyst. The concentration of ammonia water in ethanol is 2 mol / L.

[0098] 3. Sol-gel transformation: The precursor solution and alkaline catalyst were pumped into the sol-gel microchannel I through a T-shaped microchannel at a rate of 0.05 mL / min. The microchannel I had an inner diameter of 1 mm and a length of 30 cm. The organosiloxane precursor was transformed into a gel at 20 °C.

[0099] 4. The silica gel prepared in step 3 is further pumped into solvent displacement microchannel II. Microchannel II is a microtube wrapped with a microfiltration membrane with a pore size of 0.22 μm, 30 cm long and with an inner diameter of 1 mm. At the same time, ethanol is pumped into the displacement chamber at a volume flow rate of 0.1 mL / min for 2 min, and then n-hexane is pumped in at the same volume flow rate for 1 min to obtain silica wet gel.

[0100] 5. The silica wet gel prepared in step 4 is subjected to airflow spray drying at a temperature of 200℃ to obtain a hydrophilic silica aerogel.

[0101] See Figure 2 This is a sample image of the hydrophilic silica aerogel prepared in this embodiment, which can be quickly wetted by water after being immersed in water.

[0102] See Figure 3 The image shows a scanning electron microscope image of the hydrophilic silica aerogel prepared in this embodiment. As can be seen from the image, the hydrophilic silica aerogel prepared based on microchannels has the same three-dimensional network structure as the silica aerogel prepared by the traditional intermittent method, and the size of the spherical silica units is in the nanometer scale.

[0103] See Figure 4 The figure shows an optical microscope image of the hydrophilic silica aerogel prepared in this embodiment. As can be seen from the figure, the hydrophilic silica aerogel prepared based on microchannels has a size of 0.853 mm and has obvious microchannel size characteristics.

[0104] Example 2

[0105] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0106] Take 9g of TEOS and condense it in 45.6g of methanol and 6g of water to form an organosiloxane precursor solution, wherein the silicon content in the organosiloxane is 2wt%; take a certain amount of ammonia water and add it to ethanol and stir to form an alkaline catalyst, wherein the concentration of ammonia water in ethanol is 10mol / L.

[0107] All microchannels have an inner diameter of 0.5 mm. Microchannel I is 50 cm long. Solvent displacement microchannel II is a microtube made of a 0.22 μm pore size microfiltration membrane and is 50 cm long.

[0108] (1) The precursor solution and the alkaline catalyst were pumped into the sol-gel microchannel through a T-type micromixer at a rate of 1 mL / min and 2 mL / min, respectively, and the sol-gel conversion was carried out at 20 °C.

[0109] (2) The gel prepared in (1) was pumped into the solvent displacement microchannel, while ethanol was pumped into the displacement chamber at a volume flow rate of 9 mL / min for 0.5 min. Then n-heptane was pumped in at the same volume flow rate for 0.5 min.

[0110] (3) The wet gel prepared in (2) was subjected to airflow spray drying at 20°C to obtain hydrophilic silica aerogel.

[0111] See Figure 5 The image shows a scanning electron microscope image of the hydrophilic silica aerogel prepared in this embodiment. As can be seen from the image, the microstructure of the hydrophilic silica aerogel prepared based on microchannels is the same as that in Example 1.

[0112] See Figure 6 The figure shows an optical microscope image of the hydrophilic silica aerogel prepared in this embodiment. As can be seen from the figure, the hydrophilic silica aerogel prepared based on microchannels has a size of 0.417 mm.

[0113] Example 3

[0114] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0115] Take 6.8g of TMOS and stir it in 14g of DMSO to form an organosiloxane precursor solution, wherein the silicon content in the organosiloxane is 6wt%; take a certain amount of sodium hydroxide and add it to ethanol and stir to form an alkaline catalyst, wherein the concentration of sodium hydroxide in ethanol is 1mol / L.

[0116] All microchannels have an inner diameter of 0.6 mm. Microchannel I is 50 cm long, while solvent displacement microchannel II is a microtube wrapped with a 0.45 μm pore size microfiltration membrane and is 80 cm long.

[0117] (1) The precursor solution was pumped into the sol-gel microchannel through a T-type micromixer at a rate of 0.5 mL / min and the alkaline catalyst at a rate of 0.6 mL / min. The sol-gel transition was carried out at 40 °C.

[0118] (2) The gel prepared in (1) is continuously pumped into the solvent displacement microchannel, while ethanol is pumped into the displacement chamber at a rate of 55 mL / min for 1 min, and then cyclohexane is pumped in at the same volume flow rate for 1 min.

[0119] (3) The wet gel prepared in (2) was dried under normal pressure at 20°C to obtain hydrophilic silica aerogel.

[0120] Example 4

[0121] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0122] Take 13g of TMOS and stir it in 10g of DMF to form an organosiloxane precursor solution, wherein the silicon content in the organosiloxane is 10.4wt%; take a certain amount of sodium hydroxide and add it to ethanol and stir to form an alkaline catalyst, wherein the concentration of sodium hydroxide in ethanol is 6.87mol / L.

[0123] All microchannels have an inner diameter of 1 mm. Microchannel I is 100 cm long. Solvent displacement microchannel II is a microtube wrapped with a 0.45 μm pore size microfiltration membrane and is 100 cm long.

[0124] (1) The precursor solution and alkaline catalyst were pumped into the sol-gel microchannel at a rate of 10 mL / min through a T-type micromixer and the sol-gel conversion was carried out at 60 °C.

[0125] (2) The gel prepared in (1) was pumped into the solvent displacement microchannel, while ethanol was pumped into the displacement chamber at a rate of 200 mL / min for 0.05 min.

[0126] (3) The wet gel prepared in (2) was subjected to supercritical drying to obtain hydrophilic silica aerogel.

[0127] Example 5

[0128] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0129] Take 9g TEOS, 6g DMDMS, and 5.5g TMOS and condense them in 26g ethanol and 3.9g water to form an organosiloxane precursor solution, wherein the silicon content in the organosiloxane is 7.2wt%; take a certain amount of ammonia water and add it to water and stir to form an alkaline catalyst, wherein the concentration of the ammonia water in the water is 5mol / L.

[0130] All microchannels have an inner diameter of 0.8 mm. Microchannel I is 10 cm long, while solvent displacement microchannel II is a microtube wrapped with a 5 μm pore size microfiltration membrane and is 5 cm long.

[0131] (1) The precursor solution and alkaline catalyst were pumped into the sol-gel microchannel through a T-type micromixer at a rate of 0.05 mL / min, and the sol-gel conversion was carried out at 50 °C.

[0132] (2) The gel prepared in step (1) is pumped into the solvent displacement microchannel, while tert-butanol is pumped into the displacement chamber at a rate of 5 mL / min for 0.25 min.

[0133] (3) After freezing the wet gel prepared in step (2) at -12°C for 8 hours, it was placed in a vacuum freeze dryer for freeze drying to obtain hydrophilic silica aerogel.

[0134] Example 6

[0135] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0136] Take 10g TEOS and 1.4g DMDMS in 6g methanol and 1g water, and condense them to form an organosiloxane precursor solution, wherein the silicon content is 9.1wt%; weigh a certain amount of ammonia water and add it to ethanol and stir to form an alkaline catalyst, wherein the concentration of ammonia water in ethanol is 8mol / L.

[0137] All microchannels have an inner diameter of 1 mm. Microchannel I is 30 cm long. Solvent-displacement microchannels II, III, and IV are microtubes wrapped with 5 μm pore size microfiltration membranes. Microchannel II is 6 cm long, microchannel III is 5 cm long, and microchannel IV is 12 cm long.

[0138] (1) The precursor solution was pumped into the sol-gel microchannel I through a T-type micromixer at a rate of 0.3 mL / min and the alkaline catalyst at a rate of 0.2 mL / min, and the sol-gel transition was carried out at 20 °C.

[0139] (2) The gel prepared in step (1) is continuously pumped into solvent replacement microchannel II, while methanol is pumped into the first solvent replacement chamber at a rate of 4 mL / min for 1 min.

[0140] (3) The wet gel prepared in step (2) is pumped into the hydrophobic modification channel III. At the same time, TMCS is pumped into the modification chamber at a volume flow rate of 10 mL / min for 0.5 min. The gel is then fed into the second solvent replacement chamber. Methanol is pumped into the second solvent replacement chamber at a volume flow rate of 5 mL / min for 1 min, and then replaced with n-hexane for 1 min.

[0141] (4) The wet gel prepared in step (3) is spray-dried at a temperature of 100°C to obtain hydrophobic silica aerogel.

[0142] See Figure 7The image shows a scanning electron microscope image of the hydrophobic silica aerogel prepared in this embodiment. As can be seen from the image, the microstructure of the hydrophobic silica aerogel prepared based on microchannels is the same as that of the hydrophilic silica aerogels in Examples 1 and 2.

[0143] See Figure 8 Figure 1 shows the nitrogen adsorption curve of the hydrophobic silica aerogel prepared in this embodiment. As can be seen from the figure, the nitrogen adsorption-desorption isotherm of the hydrophobic silica aerogel prepared based on microchannels is a type IV-H1 hysteresis loop, which confirms that the obtained silica aerogel is composed of mesopores between micropores (less than 2 nm) and macropores (greater than 50 nm), and is a uniformly sized aggregate of spherical particles.

[0144] See Figure 9 The figure shows the micropore size distribution of the hydrophobic silica aerogel prepared in this embodiment. As can be seen from the figure, the average particle size of the hydrophobic silica aerogel prepared based on microchannels is between 15nm and 20nm, which shows that the nanoscale porous silica aerogel material was successfully prepared in this embodiment.

[0145] See Figure 10 The figure shows the TG curve of the hydrophobic silica aerogel prepared in this embodiment. As can be seen from the figure, the hydrophobic silica aerogel prepared based on microchannels has a mass retention rate of 79.1% when heated to 900℃, which shows that it has good thermal stability.

[0146] Figure 11 The figure shows the contact angle of the hydrophobic silica aerogel prepared in this embodiment. As can be seen from the figure, the hydrophobic silica aerogel prepared based on microchannels has a contact angle as high as 141.9°, which has a very good hydrophobic effect.

[0147] Example 7

[0148] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0149] Take 15g of TMOS and stir it in 1g of ethanol to form an organosiloxane precursor solution, wherein the silicon content in the organosiloxane is 17.3wt%; take a certain amount of sodium hydroxide and add it to ethanol and stir to form an alkaline catalyst, wherein the concentration of sodium hydroxide in ethanol is 2mol / L.

[0150] All microchannels have an inner diameter of 1 mm. Microchannel I is 50 cm long. Solvent-displacement microchannels II, III, and IV are microtubes wrapped with microfiltration membranes with a pore size of 0.45 μm. Microchannel II is 50 cm long, microchannel III is 50 cm long, and microchannel IV is 100 cm long.

[0151] (3) The precursor solution was pumped into the sol-gel microchannel I through a T-type micromixer at a rate of 2 mL / min and the alkaline catalyst at a rate of 1.5 mL / min, and the sol-gel conversion was carried out at 40 °C.

[0152] (4) The gel prepared in step (3) is pumped into the solvent replacement microchannel II, while ethanol is pumped into the first solvent replacement chamber at a volume flow rate of 200 mL / min for 0.1 min.

[0153] (5) The wet gel prepared in step (4) is pumped into the hydrophobic modification channel III. At the same time, HDMS is pumped into the modification chamber at a volume flow rate of 200 mL / min. The hydrophobic modification is performed for 0.1 min. Then, microchannel IV is continued to be introduced. Tert-butanol is pumped into the second solvent replacement chamber at a volume flow rate of 100 mL / min for 0.2 min.

[0154] (6) After freezing the wet gel prepared in step (2) at -12°C for 8 hours, it was placed in a vacuum freeze dryer for freeze drying to obtain hydrophobic silica aerogel.

[0155] Figure 12 The figure shows the contact angle of the hydrophobic silica aerogel prepared in this embodiment. As can be seen from the figure, the hydrophobic silica aerogel prepared based on microchannels has a contact angle as high as 125.8°, and the hydrophobic effect is good.

[0156] Example 8

[0157] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0158] Take 7.5g TEOS and 3g MTMS in 13.3g DMF and 2.6g water, and condense them to form an organosiloxane precursor solution, wherein the silicon content is 6.2wt%; weigh a certain amount of sodium hydroxide and add it to water and stir to form an alkaline catalyst, wherein the concentration of sodium hydroxide in water is 15mol / L.

[0159] All microchannels have an inner diameter of 0.8 mm. Microchannel I is 30 cm long. Solvent-displacement microchannels II, III, and IV are microtubes wrapped with 5 μm pore size microfiltration membranes. Microchannel II is 60 cm long, microchannel III is 30 cm long, and microchannel IV is 90 cm long.

[0160] (3) The precursor solution and alkaline catalyst were pumped into the sol-gel microchannel I through a T-type micromixer at a rate of 0.3 mL / min, and the sol-gel conversion was carried out at 50 °C.

[0161] (4) The gel prepared in step (3) is pumped into the solvent replacement microchannel II, while methanol is pumped into the first solvent replacement chamber at a volume flow rate of 60 mL / min for 0.5 min.

[0162] (5) The wet gel prepared in step (4) is pumped into the hydrophobic modification channel III. At the same time, HMDS is pumped into the modification chamber at a volume flow rate of 6 mL / min. After hydrophobic modification for 0.25 min, it is then introduced into the microchannel IV. Methanol is pumped into the second solvent replacement chamber at a volume flow rate of 60 mL / min for 0.75 min.

[0163] (6) The wet gel prepared in step (5) is subjected to supercritical drying to obtain hydrophobic silica aerogel.

[0164] Example 9

[0165] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0166] Take 0.5g TEOS and 20g TMOS in 0.5g DMSO and stir to form an organosiloxane precursor solution, wherein the silicon content is 17.9wt%; weigh a certain amount of concentrated ammonia water as an alkaline catalyst, wherein the ammonia water concentration is 13.3mol / L.

[0167] All microchannels have an inner diameter of 1 mm. Microchannel I is 100 cm long. Solvent-displacement microchannels II, III, and IV are microtubes wrapped with microfiltration membranes with a pore size of 0.22 μm. Microchannel II is 100 cm long, microchannel III is 100 cm long, and microchannel IV is 100 cm long.

[0168] (3) The precursor solution and alkaline catalyst were pumped into the sol-gel microchannel I through a T-type micromixer at a rate of 5 mL / min, and the sol-gel conversion was carried out at 60 °C.

[0169] (4) The gel prepared in step (3) is pumped into the solvent replacement microchannel II, while methanol is pumped into the first solvent replacement chamber at a volume flow rate of 40 mL / min for 0.1 min.

[0170] (5) The wet gel prepared in step (4) is pumped into the hydrophobic modification channel III. At the same time, TMCS is pumped into the modification chamber at a volume flow rate of 100 mL / min. The hydrophobic modification is performed for 0.1 min. Then, microchannel IV is continued to be introduced. Cyclohexane is pumped into the second solvent replacement chamber at a volume flow rate of 40 mL / min for 0.1 min.

[0171] (6) The wet gel prepared in step (5) is dried under normal pressure and dried at 80°C for 12 hours to obtain hydrophobic silica aerogel.

[0172] Example 10

[0173] Based on the microchannel mixing reaction apparatus provided in Example 1, this example provides a method for preparing silica aerogel, the specific steps of which include:

[0174] Take 3g TMOS and 17g MTMS in 0.5g DMF and condense them to form an organosiloxane precursor solution, wherein the silicon content is 20wt%; weigh a certain amount of sodium hydroxide and add it to water and stir to form an alkaline catalyst, wherein the concentration of sodium hydroxide in water is 4mol / L.

[0175] All microchannels have an inner diameter of 0.5 mm. Microchannel I is 85 cm long. Solvent-displacement microchannels II, III, and IV are microtubes wrapped with microfiltration membranes with a pore size of 0.22 μm. Microchannel II is 20 cm long, microchannel III is 30 cm long, and microchannel IV is 10 cm long.

[0176] (3) The precursor solution and the alkaline catalyst were pumped into the sol-gel microchannel I through a T-type micromixer at a rate of 0.07 mL / min and 0.03 mL / min, respectively, and the sol-gel conversion was carried out at 40 °C.

[0177] (4) The gel prepared in step (3) is pumped into solvent replacement microchannel II, while ethanol is pumped into the replacement chamber at a volume flow rate of 5 mL / min for 0.33 min.

[0178] (5) The wet gel prepared in step (4) is pumped into the hydrophobic modification channel III. At the same time, HMDSO is pumped into the modification chamber at a volume flow rate of 20 mL / min. The hydrophobic modification is carried out for 0.5 min. Then, microchannel IV is continued to be introduced. Cyclohexane is pumped into the second solvent replacement chamber at a volume flow rate of 1 mL / min for 0.2 min.

[0179] (6) The wet gel prepared in step (5) is dried at normal pressure and dried at 200°C for 2 hours to obtain hydrophobic silica aerogel.

[0180] Comparative Example 1

[0181] Silica aerogels were prepared using a conventional batch process under the same conditions for comparison with Example 1. The specific preparation process is as follows:

[0182] 1. Preparation of organosiloxane precursor solution: 15g TEOS was polycondensed in 13.3g ethanol and 2.5g water to form organosiloxane precursor solution. The silicon content in the organosiloxane was 6.6wt%.

[0183] 2. Preparation of catalyst: A certain amount of ammonia water is added to ethanol and stirred to form an alkaline catalyst. The concentration of ammonia water in ethanol is 2 mol / L.

[0184] 3. Sol-gel transformation: Take 1 mL of precursor solution and 1 mL of alkaline catalyst, pour them into a glass bottle and stir to mix. Let stand at 20°C and wait for the sol-gel transformation to obtain a gel.

[0185] 4. Replace the silica gel prepared in step 3 with 2 mL of ethanol 10 times, with an interval of 30 min between each replacement; then use 2 mL of ethanol...

[0186] The silica wet gel was obtained by replacing the silica gel with hexane twice, with a 30-minute interval between each replacement.

[0187] 5. The silica wet gel prepared in step 4 is subjected to airflow spray drying at a temperature of 200℃ to obtain a hydrophilic silica aerogel.

[0188] See Figure 13 The figures show infrared images of silica aerogels prepared using microchannel technology and intermittent technology in Examples 1 and 1 of this invention, respectively. As can be seen from the figures, the silica aerogels located at 1100 cm⁻¹... -1 The strong and broad Si-O vibrational peak at 3200 cm⁻¹ indicates the presence of numerous -Si-O-Si- groups in the silica aerogel. -1 The OH vibration peak at 2900 cm⁻¹ indicates the presence of -OH groups in the aerogel. -1 and 1200cm -1 The corresponding tensile and bending vibrations are the peaks of CH bonds. Combined with the electron microscopy and optical microscopy images of Example 1, it is clear that the silica aerogel obtained using the technical solution of this invention has the same three-dimensional porous network structure and chemical bond composition as silica prepared by intermittent methods in the prior art.

[0189] Comparative Example 2

[0190] Silica aerogels were prepared using a conventional batch process under the same conditions for comparative Example 6. The specific preparation process is as follows:

[0191] Take 10g TEOS and 1.4g DMDMS in 6g methanol and 1g water, and condense them to form an organosiloxane precursor solution, wherein the silicon content is 9.1wt%; weigh a certain amount of ammonia water and add it to ethanol and stir to form an alkaline catalyst, wherein the concentration of ammonia water in ethanol is 8mol / L.

[0192] (1) Take 1.5 mL of precursor solution and 1 mL of alkaline catalyst, stir and mix them in a glass bottle, and let stand at 20°C to wait for the sol-gel transformation.

[0193] (2) Replace the gel prepared in step (1) with 20 mL of methanol 6 times, with an interval of 30 min each time.

[0194] (3) Modify the wet gel prepared in step (2) with 20 mL TMCS for 30 min; then replace it with 25 mL methanol 6 times, with an interval of 30 min each time, and then replace it with 25 mL n-hexane once.

[0195] (4) The wet gel prepared in step (5) is spray-dried at a temperature of 100°C to obtain hydrophobic silica aerogel.

[0196] See Figure 14 The image shows the contact angle of the hydrophobic silica aerogel prepared in this comparative example. As can be seen from the image, the contact angle is 138.5°, indicating good hydrophobicity. In contrast, the hydrophobic silica aerogel prepared based on microchannels in Example 6 has a contact angle of 141.9°, demonstrating that the silica aerogel prepared based on microchannels exhibits the same hydrophobic effect as silica aerogels prepared using traditional intermittent methods. Furthermore, the total solvent volume required for solvent replacement in this comparative example is 118 times the volume of the wet gel, and the total replacement time is 360 minutes. In contrast, in Example 6, the total solvent volume required for dynamic solvent replacement within the microchannels is 28 times the volume of the wet gel, and the total replacement time is 3 minutes. This indicates that dynamic solvent replacement based on microchannels can significantly save solvent and reduce the time required for solvent replacement, thus significantly improving solvent replacement efficiency.

[0197] Furthermore, the physical properties of the examples and comparative examples were tested, including the density, specific surface area, pore volume, contact angle, and thermal conductivity of the prepared silica aerogels.

[0198] The characterization images (including electron microscopy, optical photographs, pore volume, etc.) in the above embodiments, combined with the data analysis results in Table 1, show that the silica aerogel prepared based on microchannels has the same high specific surface area and pore volume as silica aerogel prepared by the traditional batch method, as well as excellent heat resistance. Moreover, the hydrophobically modified silica aerogel can achieve the same hydrophobic effect.

[0199] Furthermore, comparing the solvents used in the examples and comparative examples reveals that solvent replacement in the microchannels can save a significant amount of solvent and greatly reduce the replacement time, thus significantly improving solvent replacement efficiency.

[0200] Table 1 Performance test results of the examples and comparative examples

[0201]

[0202] As shown in Table 1, the silica aerogel prepared based on microchannels exhibits the same low thermal conductivity, extremely low density, and extremely high specific surface area as silica aerogel prepared by the traditional batch method under the same conditions, further demonstrating the feasibility of the microchemical method.

[0203] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A continuous process for the preparation of silica aerogels based on microchannel technology, characterized in that, This includes continuously feeding raw materials into a microchannel mixing reactor, continuously performing sol-gel transformation and solvent replacement, drying to generate silica aerogel, and continuously outputting the aerogel; The microchannel mixing reaction device includes at least a continuous sol-gel transition section and a first solvent replacement section; The continuous sol-gel transition section is a T-shaped microchannel, including multiple input ends arranged in parallel, a T-shaped micromixer for mixing reaction raw materials, and microchannel I; The first solvent replacement section includes a microchannel II and a first solvent replacement chamber connected together, wherein the microchannel II is disposed within the first solvent replacement chamber; After the reaction raw materials are fed into the input end, they are mixed evenly in the T-type micro mixer, and then enter the microchannel I to carry out a continuous sol-gel reaction to obtain sol-gel products; The sol-gel product enters the microchannel II, and at the same time, a replacement solvent is injected into the first solvent replacement chamber to perform solvent replacement and obtain a wet gel.

2. The continuous production process according to claim 1, characterized in that, The organosiloxane precursor solution and the alkaline catalyst are mixed evenly through the T-type micro mixer via different input terminals and then pumped into microchannel I at a total volumetric flow rate of 0.1 mL / min to 20 mL / min. The length of the microchannel I is 10 cm to 100 cm; the inner diameter is 0.1 mm to 1 mm. The microchannel II is a microtube wrapped with a microfiltration membrane; The microfiltration membrane contains micropores with a pore size of 0.22 μm to 5 μm; The inner diameter of the microtube is the same as the inner diameter of the microchannel I; the length of the microchannel II is 5 cm to 100 cm; The sol-gel reaction conditions include: a reaction temperature of 20 ℃ to 60 ℃; The organosiloxane precursor solution comprises an organosiloxane monomer and an organic solvent; The silicon content in the organosiloxane precursor solution is 2 wt%~20 wt%; The alkaline catalyst includes either ammonia or sodium hydroxide solution; The solvent of the alkaline catalyst includes either ethanol or water, and the concentration of the base in the alkaline catalyst is 1 mol / L to 15 mol / L. The organosiloxane monomer includes any one or a combination of two or more of tetraethyl orthosilicate, tetramethyl orthosilicate, methyltrimethoxysilane, and dimethyldimethoxysiloxane. The organic solvent includes any one or a combination of two or more of methanol, ethanol, dimethylformamide, dimethyl sulfoxide, and water; The replacement solvent is selected from any one or a combination of two or more of methanol, ethanol, tert-butanol, n-hexane, n-heptane, and cyclohexane; The volumetric flow rate of the displacement solvent input or output is 0.1 mL / min to 200 mL / min.

3. The continuous production process of claim 1, wherein, The microchannel I is made of PTFE capillary.

4. The continuous preparation method according to claim 1, characterized in that, The material of the microchannel II is PTFE.

5. The continuous preparation method according to claim 1, characterized in that, The microchannel mixing reaction device further includes a modification section, which includes microchannel III and a modification chamber, microchannel IV and a second solvent replacement chamber; The microchannel III is placed inside the modified cavity and connected to the first solvent replacement cavity; The microchannel IV is placed inside the second solvent replacement chamber and connected to the modification chamber; A modifier is introduced into the modification cavity, and the wet gel enters the microchannel III for surface modification; then, it continues to enter the microchannel IV, and the solvent replacement operation is repeated to obtain the modified wet gel.

6. The continuous preparation method according to claim 5, characterized in that, Microchannel III and microchannel IV are extensions of microchannel II, and have the same inner diameter; The replacement solvent is dynamically input or output to the first solvent replacement chamber and / or the second solvent replacement chamber; The modifier is input into or output into the modification cavity in a dynamic manner.

7. The continuous preparation method according to claim 5, characterized in that, The microchannel III or the microchannel IV is 5 cm to 100 cm long.

8. The continuous preparation method according to claim 5, characterized in that, The volumetric flow rate of the displacement solvent and / or the modifier input or output is 0.1 mL / min to 200 mL / min.

9. The continuous preparation method according to claim 5, characterized in that, The replacement solvent is selected from any one or a combination of two or more of methanol, ethanol, tert-butanol, n-hexane, n-heptane, and cyclohexane; The modifier is a hydrophobic modifier selected from any one or a combination of two or more of trimethylchlorosilane, hexamethyldisilazane, and hexamethyldisiloxane.

10. The continuous preparation method according to any one of claims 1-9, characterized in that, The drying process includes supercritical drying, freeze drying, atmospheric pressure drying, and / or airflow spray drying.

11. The continuous preparation method according to claim 10, characterized in that, The supercritical drying process includes: replacing the liquid components inside the gel material with a supercritical fluid in a supercritical state to obtain an aerogel material. The supercritical fluid used includes any one of supercritical CO2, supercritical methanol, and supercritical ethanol.

12. The continuous preparation method according to claim 10, characterized in that, The atmospheric pressure drying includes: replacing the pore solution in the wet gel with one or more low surface tension solvents, and evaporating the solvent under atmospheric pressure to obtain an aerogel material; The evaporation temperature is 20 ℃ to 200 ℃.

13. The continuous preparation method according to claim 10, characterized in that, The airflow spray drying process involves thoroughly mixing the gel material with natural air and then evaporating and drying it. The temperature of the natural air is 20 ℃ to 200 ℃.

14. The continuous preparation method according to claim 10, characterized in that, The freeze-drying includes vacuum freeze-drying under reduced pressure; The vacuum freeze-drying process involves freezing the gel material below its freezing point and then sublimating the solvent under a high vacuum to obtain an aerogel material.

15. The continuous preparation method according to claim 14, characterized in that, The vacuum freezing method includes: pre-freezing in a freezing device and freezing directly in a drying chamber by rapid vacuuming; The cold trap temperature for the vacuum freeze-drying process is -45 ℃ to -80 ℃, and the vacuum degree is less than 0.1 kPa.

16. A microchannel mixing reaction apparatus for preparing silica aerogel using the continuous preparation method according to any one of claims 1-15, characterized in that, It includes at least a continuous sol-gel transition section and a first solvent replacement section. The continuous sol-gel transition section is a T-shaped microchannel, including multiple input ends arranged in parallel, a T-shaped micromixer for mixing reaction raw materials, and a microchannel I connected to the sample injection unit. The first solvent replacement section includes a microchannel II and a first solvent replacement chamber connected in parallel, and the microchannel II is disposed in the first solvent replacement chamber. The microchannel I is made of PTFE capillary; the length of the microchannel I is 10 cm to 100 cm; the inner diameter of the microchannel I is 0.1 mm to 1 mm. The microchannel II is a microtube wrapped with a microfiltration membrane; the micropores contained in the microfiltration membrane have a pore size of 0.22 μm to 5 μm; the inner diameter of the microtube is the same as the inner diameter of the microchannel I; the length of the microchannel II is 5 cm to 100 cm.

17. The microchannel mixing reaction apparatus according to claim 16, characterized in that, It also includes a modification section and a second solvent replacement section; the modification section and the second solvent replacement section are multiple repeating units that modify the surface of the wet gel material; The modified section includes microchannel III and a modified cavity, microchannel IV and a second solvent replacement cavity; The microchannel III is placed inside the modified cavity and connected to the first solvent replacement cavity; The microchannel IV is placed inside the second solvent replacement chamber and connected to the modification chamber; Microchannel III and microchannel IV are extensions of microchannel II; the length of microchannel III or microchannel IV is 5 cm to 100 cm.

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