CN118515288A

CN118515288A - Silicon dioxide aerogel based on micro-channel technology and preparation method and device thereof

Info

Publication number: CN118515288A
Application number: CN202410605293.XA
Authority: CN
Inventors: 张学同; 王倩楠
Original assignee: Suzhou Institute of Nano Tech and Nano Bionics of CAS
Current assignee: Suzhou Institute of Nano Tech and Nano Bionics of CAS
Priority date: 2024-05-15
Filing date: 2024-05-15
Publication date: 2024-08-20

Abstract

The invention provides a silicon dioxide aerogel based on a micro-channel technology and a preparation method and a device thereof; the preparation method comprises the steps of continuously inputting raw materials into a micro-channel mixing reaction device, continuously performing sol-gel conversion, solvent replacement and hydrophobic modification, drying to obtain silica aerogel, and continuously outputting. By adopting the technical scheme of the invention, the micro-gel can be formed by rapidly mixing the reaction materials by utilizing the extremely high specific surface area of the micro-channel; the mass transfer efficiency is high by utilizing the micro-channel, the solvent replacement and hydrophobic modification time can be greatly shortened, and a large amount of solvent is saved; compared with the traditional intermittent preparation method of the silicon dioxide aerogel, the preparation method integrates the preparation process into a single micro-channel system, solves the problems of multi-step dispersion and discontinuity, and has the advantages of being independent of each other, detachable, combinable, flexible and efficient.

Description

Silicon dioxide aerogel based on micro-channel technology and preparation method and device thereof

Technical Field

The invention relates to the technical field of nano porous materials, in particular to a preparation method of a nano porous aerogel material, and more particularly relates to a silicon dioxide aerogel based on a micro-channel technology and a preparation method and a device thereof

Background

Aerogel in 1931 by the university of Stanford S.S. Kistler first proposed the concept of replacing the liquid phase in the gel with the gas phase and invented silica aerogel. However, limited by the high threshold of aerogel production technology, its development has almost stagnated for about thirty years. Until 1966, j.b.peri. Use of alkoxysilane instead of sodium silicate in Kistler work, silica aerogel was prepared by a one-step sol-gel method using a silicone ester, rapidly promoting the progress of research in the aerogel field. Aerogels are classified into three categories based on the framework composition: inorganic aerogels (including silica aerogels and metal oxide aerogels), organic aerogels (precursors are mostly resorcinol-formaldehyde) and carbon aerogels. Among them, silica aerogel is represented. The silica aerogel nano porous structure has the pore range of 5-150nm, the average pore diameter of 20-40nm, the characteristics of low density, high porosity, high specific surface area, low heat conductivity and the like, and has wide application prospects in the fields of heat insulation, catalyst carriers, optics and the like (Nature, 1931, 127 (3211): 741-741;The Journal of Physical Chemistry,1966, 70 (9): 2937-2945).

The preparation process of the aerogel comprises the following steps: (1) sol-gelation. The method is a core process for preparing aerogel, precursor is hydrolyzed and condensed under the action of a catalyst to form gel, and the regulation and control of the microstructure of a gel skeleton can be realized by adjusting reaction conditions; (2) aging. The method is a process of dissolving and re-polycondensing heterogeneous gel particles, so that the connection between secondary particles is enhanced, larger agglomerate particles are obtained, and the effect of enhancing the aerogel framework is achieved; (3) solvent displacement. The preparation is carried out for the subsequent drying process, and a large amount of solvent with smaller surface tension is used for replacing the moisture in the gel, so that the nano powder with better dispersibility can be obtained.

Taking silica as an example, the current silica aerogel preparation method comprises a one-step method and a two-step method (Particle & PARTICLE SYSTEMS Characterization, 2023:2200186). The one-step method is to blend a molecular precursor, water, a solvent and a catalyst acid or alkali, put the mixture in a container, stand for a certain time to wait for the slow formation of gel, and regulate the size of the nano construction unit by adding a surfactant. While precursors like TMOS, TEOS, etc., require large amounts of solvents to dilute the silica sol, one-step methods limit aerogel formation, and two-step methods have been proposed as a solution strategy. In the first stage of the two-step process, the precursor undergoes hydrolytic condensation by means of an acid catalyst; hydrolysis and immobilization are then accomplished with a non-alcoholic solution such as acetone or the like to form silica aerogel. The two-step method can control the pore structure of the silica aerogel to be highly controllable, and can avoid the technical problems caused by solvent dilution by the one-step method, thereby being the preferred technical means for preparing the standard aerogel structure at present.

However, in the prior art, the conventional two-step method is adopted to prepare the aerogel, which is generally a batch preparation process, and the process has the problems of discontinuity, non-integration, large size of the aerogel and the like, so that the mass transfer and heat transfer performance of the aerogel are greatly limited, and the solvent consumption in a solvent replacement link is also large, so that the problem of solvent waste exists. Further, the preparation of silica aerogel in the prior art is the same as the above problems, and the problems of complicated preparation process caused by discontinuous and multi-step dispersion, waste of a great deal of manpower and material resources, low production efficiency, high production cost, and especially, the problems of long stirring time of reaction products, slow, even incomplete and insufficient solvent replacement process and the like caused by unstable quality and heat transfer due to large-size aerogel are urgent.

On the other hand, the micro-chemical technology is a technological front field of the crossing of more disciplines which is raised in the beginning of the 90 th century. In recent decades, research and application of micro-chemical technology such as micro-mixing and multiphase micro-flow, micro-heat exchange and mass transfer, micro-scale reaction and the like are developed at home and abroad, and the micro-chemical technology opens a new era of chemical engineering high-efficiency refinement. The core of the micro-chemical technology is a micro-channel reactor, which takes a micro-structure unit as a core, strengthens mixing and transmission by reducing the dispersion scale of a system, improves the process controllability and efficiency, and takes 'quantity amplification' as a basic criterion to amplify micro equipment so as to directly apply laboratory achievements to industrial processes and realize large-scale production. The research of the micro-chemical technology is carried out to enhance the safety of chemical process, promote the strengthening of the process and the miniaturization of chemical systems, improve the energy and resource utilization efficiency, and have wider application prospect. The microfluidic technology is used as one of the cores of the micro-chemical industry, can accurately control and process the micro-volume multiphase flow in the micro-channel, and provides possibility for realizing the efficient and controllable micro-chemical industry process. The use of microfluidics has expanded from the early use of analytical chemistry and inkjet printing to the emerging front of fields of synthesis of fine chemicals and new materials, high throughput analysis, simulation of cells and intracellular systems, and the like.

Chinese patent CN108975342a discloses a method for continuously preparing silica aerogel balls by using a vibrating hydrophobic surface, which comprises pumping out the mixed solution through a syringe, dripping on a vibrating hydrophobic vibrating disk to form gel, transferring the silica wet gel, aging, replacing the solvent, hydrophobically modifying and drying to obtain silica aerogel balls. The method aims to solve the problems that the SiO ₂ aerogel ball is low in efficiency, cannot be continuously produced, and is poor in quality and the like in the preparation process, but the preparation method is not related to a micro-channel technology although a syringe is used, and is completely different from the method disclosed by the invention in that the raw materials are firstly mixed for reaction and then are subjected to gel conversion by means of vibration. The Chinese patent CN105289431B discloses a preparation method of a porous NIPAAm aerogel microcapsule, which comprises the steps of taking a transparent solution containing NIPAAm monomers as a disperse phase, taking an oily substance mixed solution as a continuous phase, inputting the two into a T-shaped microchannel by a syringe according to a certain mass ratio to obtain a mixed solution containing the microcapsule, and then standing, cleaning and freeze-drying to obtain the porous NIPAAm aerogel microcapsule; the method prepares gel droplets in a microchannel and performs gel separation and collection at the outlet of the microchannel. Chinese patent No. 109650396A discloses a preparation method of silica aerogel, which uses ethanol/water as a solvent to react silica with sodium hydroxide to generate modified sodium silicate, then adds inorganic acid to generate modified silica sol by the modified sodium silicate solution, removes inorganic salt byproducts, generates modified silica gel at a certain temperature and pressure, uses nonpolar solvent to exchange solvent for the modified silica gel, and dries to obtain hydrophobic aerogel material; the method is a traditional batch preparation process, each preparation step is carried out independently, and the preparation process is discontinuous.

Based on the method, the invention provides a method for preparing the silicon dioxide aerogel by adopting a micro-chemical technology, and the safety of a micro-reactor is utilized to rapidly mix reaction materials, provide uniform reaction concentration, uniform reaction time and uniform temperature, realize rapid heat exchange, have no amplification effect and are expected to realize the continuity, integration and high efficiency of the preparation process of the silicon dioxide aerogel; compared with the prior art, the invention does not need to introduce an oil phase into the micro-channel, so that a flushing and removing process is not needed later, the reaction raw material is subjected to sol-gel reaction in the micro-channel to finish liquid-solid conversion, the full utilization of the reaction raw material is ensured, and the macroscopic size of the obtained aerogel is related to the inner diameter size of the micro-channel, therefore, the invention provides a novel method for carrying out dynamic solvent replacement in the micro-channel.

Disclosure of Invention

The invention discloses a silicon dioxide aerogel based on a micro-channel technology and a preparation method and a device thereof, which are used for overcoming the defects of the prior art.

In order to achieve the above purpose, the invention provides a continuous preparation method of silica aerogel based on a micro-channel technology, which comprises the steps of continuously inputting raw materials into a micro-channel mixing reaction device, continuously performing sol-gel conversion and solvent replacement, drying to generate silica aerogel, and continuously outputting.

Preferably, the microchannel mixing reaction device at least comprises a continuous sol-gel transition section and a first solvent replacement section; the continuous sol-gel transition section is a T-shaped micro-channel and comprises a plurality of input ends which are arranged in parallel, a T-shaped micro-mixer for mixing reaction raw materials and a micro-channel I connected with the T-shaped micro-mixer; the length of the micro-channel I is 10 cm-100 cm; the inner diameter of the micro-channel I is 0.1 mm-1 mm; the first solvent displacement section comprises a microchannel II; the micro-channel II is a micro-tube wrapped by a PTFE micro-filtration membrane; the aperture of the micropores in the microfiltration membrane is 0.22-5 mu m; the inner diameter of the micro-tube is the same as the inner diameter of the micro-channel I; the length of the micro-channel II is 5 cm-100 cm.

Preferably, the reaction raw materials enter the micro-channel I for continuous sol-gel reaction after being input into the input end, so as to obtain a sol-gel product; and the sol-gel product enters the micro-channel II, and meanwhile, a replacement solvent is injected into the first solvent replacement cavity for solvent replacement, so that wet gel is obtained.

Preferably, the organosiloxane precursor solution and the alkaline catalyst are pumped into the micro-channel I through different input ends, and the total pumping volume flow is 0.1 mL/min-20 mL/min. It is understood that the rate at which liquid is pumped into the microchannel is the flow rate of the liquid into the microchannel for reaction.

Preferably, the sol-gel reaction conditions include: the reaction temperature is 20-60 ℃.

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

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

Preferably, the organosiloxane monomer comprises tetraethyl orthosilicate, tetramethyl orthosilicate, methyl trimethoxy silane, dimethyl dimethoxy siloxane or a combination of two or more.

Preferably, the alkaline catalyst comprises one of ammonia water or sodium hydroxide solution; the solvent of the alkaline catalyst comprises one of ethanol and water, and the concentration of alkali in the alkaline catalyst is 1 mol/L-15 mol/L.

Preferably, the organic solvent comprises any one or more of methanol, ethanol, dimethylformamide, dimethyl sulfoxide and water.

Preferably, the displacement solvent is selected from any one or a combination of more than two of methanol, ethanol, tertiary butanol, n-hexane, n-heptane and cyclohexane.

Preferably, the volume flow of the input or output of the displacement solvent is 0.1 mL/min-200 mL/min.

Preferably, the microchannel mixing reaction device further comprises a modification section, wherein the modification section comprises a microchannel III, a modification cavity, a microchannel IV and a second solvent replacement cavity; the micro-channel III is arranged in the modification cavity and is connected with the first solvent replacement cavity;

the micro-channel IV is arranged in the second solvent replacement cavity and is connected with the modification cavity.

Preferably, a modifying agent is input into the modifying cavity, and the wet gel enters the micro-channel III for surface modification; then, the mixture is continuously introduced into the micro-channel IV, and the solvent replacement operation is repeated, so that the modified wet gel is obtained.

Preferably, the microchannel III and the microchannel IV are extension sections of the microchannel II, the microchannel III and the microchannel IV having the same inner diameter as the microchannel II; the length of the micro-channel III or the micro-channel IV is 5 cm-100 cm.

Preferably, the volume flow of the replacement solvent and/or the modifier input or output is 0.1 mL/min-200 mL/min.

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

Preferably, the displacement solvent is input or output to or from the first solvent displacement chamber and/or the second solvent displacement chamber in a dynamic in-out manner.

Preferably, the modifying agent is input into or output from the modifying cavity in a dynamic in-out mode.

Preferably, the drying comprises supercritical drying, freeze drying, atmospheric drying and/or air-flow spray drying.

Specifically, the supercritical drying includes: and (3) replacing liquid components in the gel material with a supercritical fluid in a supercritical state to obtain the aerogel material, wherein the supercritical fluid comprises any one of supercritical CO ₂, supercritical methanol and supercritical ethanol.

Preferably, the freeze-drying comprises vacuum freeze-drying under reduced pressure; the vacuum freeze drying comprises the steps of freezing a gel material to below a freezing point, and sublimating a solvent under a higher vacuum to obtain an aerogel material; preferably, the method of freezing comprises: freezing in the freezing device and directly and rapidly vacuumizing in the drying chamber to freeze; more preferably, the cold trap temperature of the vacuum freeze drying is-45 ℃ to-80 ℃ and the vacuum degree is less than 0.1kPa.

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

Preferably, the airflow type spray drying comprises evaporating and drying after fully mixing gel materials with natural air; the temperature of the natural air is 20-200 ℃.

The silica aerogel prepared by the preparation method has the density of 0.04g/cm ³～0.3g/cm³, the size of 0.1-1 mm, the specific surface area of 500m ²/g～1200m²/g and the thermal conductivity of 0.015W/mk-0.045W/mk.

The invention also provides a microchannel mixing reaction device for preparing silica aerogel, which at least comprises a continuous sol-gel conversion section and a first solvent replacement section, wherein the continuous sol-gel conversion section is a T-shaped microchannel, and comprises a plurality of input ends which are arranged in parallel, a T-shaped micromixer for mixing reaction raw materials and a microchannel I connected with the T-shaped micromixer; the first solvent replacement section comprises a micro-channel II and a first solvent replacement cavity which are connected, and the micro-channel II is arranged in the first solvent replacement cavity.

Preferably, the micro-channel I is a PTFE capillary; the length of the micro channel I is 10 cm-100 cm; the inner diameter of the micro-channel I is 0.1 mm-1 mm.

The micro-channel II is a micro-tube wrapped by a PTFE micro-filtration membrane; the aperture of the micropores contained in the microfiltration membrane is 0.22-5 mu m; the inner diameter of the micro-tube is the same as the inner diameter of the micro-channel I; the length of the micro-channel II is 5 cm-100 cm.

As one of the preferred embodiments, the microchannel mixing reaction device further comprises a modification section and a second solvent replacement section; the modification section and the second solvent replacement section may be a plurality of repeating units to surface modify the wet gel material; the modification section comprises a micro-channel III, a modification cavity, a micro-channel IV and a second solvent replacement cavity; the micro-channel III is arranged in the modification cavity and is connected with the first solvent replacement cavity; the micro-channel IV is arranged in the second solvent replacement cavity and is connected with the modification cavity.

Preferably, the microchannel III and the microchannel IV are extension of the microchannel II; the length of the micro-channel III or the micro-channel IV is 5 cm-100 cm.

Compared with the prior art, the invention has the advantages that:

1. According to the preparation method of the silica aerogel based on the micro-channel mixing reaction device, provided by the technical scheme of the invention, the micro-gel can be formed by rapidly mixing reaction materials by utilizing the extremely high specific surface area of the micro-channel; the mass transfer efficiency is high by utilizing the micro-channel, the solvent replacement and hydrophobic modification time can be greatly shortened, and a large amount of solvent is saved; compared with the traditional intermittent aerogel preparation method, the method integrates the preparation process into a single micro-channel system, solves the problems of multi-step dispersion and discontinuity, and has the advantages of independent, detachable and combinable links, flexibility and high efficiency.

2. By adopting the technical scheme of the invention, the micro-channel-based mixed reaction device has the characteristics of small amplification effect and simple reaction system, and is easy for continuous large-scale production.

3. By adopting the technical scheme of the invention, the advantages of rapid micro-channel mixing, high mass transfer efficiency and high integration of the preparation process can be fully exerted, the preparation of the silica aerogel can be completed in one day, the preparation period of the aerogel is greatly shortened, a large amount of solvents are saved, the production efficiency is improved, and the production cost is reduced.

5. By adopting the method for continuously preparing the silica aerogel based on the micro-channel, which is provided by the invention, a continuous operation mode of continuous feeding, continuous reaction and continuous discharging can be realized through the micro-channel, the production efficiency is improved, and the continuity, integration and high efficiency of the preparation process of the silica aerogel are realized.

5. The technical scheme of the invention has the advantages of simple preparation process, mild and controllable reaction conditions, low energy consumption, green and pollution-free performance, suitability for large-scale production and wide application prospect.

Drawings

FIG. 1 is a flow chart of the continuous preparation of silica aerogel based on the microchannel mixing reaction device of the present invention.

FIG. 2 is a sample graph of the hydrophilic silica aerogel prepared in example 1 of the present invention.

FIG. 3 is a scanning electron microscope image of the hydrophilic silica aerogel prepared in example 1 of the present invention.

FIG. 4 is an optical microscopic image of the hydrophilic silica aerogel prepared in example 1 of the present invention.

FIG. 5 is a scanning electron microscope image of the hydrophilic silica aerogel prepared in example 2 of the present invention.

FIG. 6 is an optical microscopic image of the hydrophilic silica aerogel prepared in example 2 of the present invention.

FIG. 7 is a scanning electron microscope image of the hydrophobic silica aerogel prepared in example 6 of the present invention.

FIG. 8 is a graph showing the nitrogen adsorption of the hydrophobic silica aerogel prepared in example 6 of the present invention.

FIG. 9 is a graph showing pore size distribution of the hydrophobic silica aerogel prepared in example 6 of the present invention.

FIG. 10 is a graph showing the TG curve of the hydrophobic silica aerogel prepared in example 6 of the present invention.

FIG. 11 is a graph showing the contact angle of the hydrophobic silica aerogel prepared in example 6 of the present invention.

FIG. 12 is a graph showing the contact angle of the hydrophobic silica aerogel prepared in example 7 of the present invention.

FIG. 13 is an infrared spectrum of the hydrophilic silica aerogel prepared in example 1 and comparative example 1 of the present invention.

FIG. 14 is a graph showing the contact angle of the hydrophobic silica aerogel prepared in comparative example 2 according to the present invention.

Detailed Description

The objects, technical solutions and advantages of the embodiments of the present application will be more apparent, and the technical solutions in the embodiments of the present application will be clearly and completely described, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to fall within the scope of the application.

The invention provides a method for continuously preparing silica aerogel based on micro-channels, which comprises the following steps: continuously inputting a precursor solution, an alkaline catalyst, a solvent and a modifier for preparing the silica aerogel into a T-shaped micro-channel, continuously performing sol-gel conversion, solvent replacement and hydrophobic modification, and continuously outputting the silica gel generated in the micro-channel; and then drying to obtain the silica aerogel, and continuously outputting.

Further, the method for continuously preparing the silica aerogel based on the micro-channels comprises the following steps:

(1) Pumping an organosiloxane precursor solution and an alkaline catalyst into a T-shaped microchannel in a certain volume flow rate, and performing continuous sol-gel conversion at a certain reaction temperature;

(2) Continuously feeding the obtained wet gel into a solvent replacement microchannel II, and simultaneously inputting a replacement solvent into a replacement cavity I at a certain volume flow, wherein the solvent adopts a dynamic inlet and outlet mode;

steps (3) and (4), optionally with or without, comprise:

(3) Continuously feeding the obtained wet gel into a hydrophobic modification microchannel III, and simultaneously inputting a modifier into a displacement cavity II at a certain volume flow, wherein the modifier adopts a dynamic inlet and outlet mode;

(4) Continuously feeding the obtained wet gel into a solvent replacement microchannel IV, and simultaneously inputting a solvent into a replacement cavity III at a certain volume flow, wherein the solvent adopts a dynamic inlet and outlet mode;

(5) And carrying out special drying on the wet gel to obtain the silica aerogel.

In some embodiments, the organosiloxane precursor solution includes an organosiloxane monomer and a solvent.

Further, the organic siloxane monomer comprises any one or more than two of tetraethoxysilane, tetramethyl orthosilicate, methyltrimethoxysilane and dimethyl dimethoxy siloxane; the solvent comprises any one or more than two of methanol, ethanol, dimethylformamide, dimethyl sulfoxide and water, and the content of silicon in the organic siloxane precursor solution is 2-20wt%.

In some embodiments, the alkali in the alkaline catalyst comprises one of ammonia water or sodium hydroxide, the solvent of the alkaline catalyst comprises one of ethanol and water, and the concentration of the alkali in the alkaline catalyst is 1mol/L to 15mol/L.

In some embodiments, the organosiloxane precursor solution and the basic catalyst are pumped into the microchannel apparatus at a total volume flow rate of 0.1mL/min to 20 mL/min.

In some embodiments, the sol-gel reaction temperature is from 20 ℃ to 60 ℃.

In some embodiments, the displacement solvent is selected from any one or a combination of two or more of methanol, ethanol, t-butanol, n-hexane, n-heptane, cyclohexane.

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

In some embodiments, the microchannel I is a PTFE capillary; the length of the micro channel I is 10 cm-100 cm; the inner diameter of the micro-channel I is 0.1 mm-1 mm.

In some embodiments, the microchannel II is a microtube wrapped with a PTFE microfiltration membrane; the aperture of the micropores contained in the microfiltration membrane is 0.22-5 mu m; the inner diameter of the microtube is the same as the inner diameter of the micro-channel I; the length of the micro-channel II is 5 cm-100 cm.

In some embodiments, the microchannel III or the microchannel IV is an extension of the microchannel II; the length of the micro-channel III or the micro-channel IV is 5 cm-100 cm.

In some embodiments, the displacement solvent and/or the modifier input or output volume flow is from 0.1mL/min to 200mL/min.

In some embodiments, the special drying means includes supercritical drying, freeze drying, atmospheric drying, and air-flow spray drying; and/or supercritical drying is characterized in that the liquid component in the gel material is replaced by supercritical fluid in a supercritical state to obtain aerogel material, wherein the supercritical fluid comprises any one of supercritical CO ₂, supercritical methanol and supercritical ethanol; and/or freeze-drying techniques including vacuum freeze-drying and reduced pressure drying, characterized in that the gel material is frozen below freezing point, and then the solvent is sublimated under higher vacuum to obtain aerogel material; and/or the freezing method comprises: the freezing device is pre-frozen and the drying chamber is directly vacuumized to be frozen. The cold trap temperature of vacuum freeze drying is-45 ℃ to-80 ℃ and the vacuum degree is less than 0.1kPa; and/or the normal pressure drying technique is characterized in that one or more solvents with low surface tension are used for replacing pore solution in wet gel, and the solvent is evaporated under normal pressure and a certain temperature (20 ℃ to 200 ℃) to obtain aerogel materials; and/or the air flow type spray drying technology is characterized in that the gel material is fully mixed with the heated natural air (20-200 ℃), and the aim of evaporation drying is achieved in a short time due to the large heat and mass exchange area. Particularly preferred are atmospheric drying techniques and air-flow spray drying techniques.

In some embodiments, the silica aerogel has a density of 0.04g/cm ³～0.3g/cm³, a size of 0.1mm to 1mm, a specific surface area of 500m ²/g～1200m²/g, and a thermal conductivity of 0.015W/mk to 0.045W/mk.

According to the method for continuously preparing the silica aerogel by the micro-channels, which is provided by the technical scheme, continuous industrial production of the preparation of the silica aerogel can be realized, raw materials and aerogel products of the silica aerogel continuously enter and exit in the micro-channels, the micro-channels are utilized for rapid mixing, the mass transfer efficiency is high, and the problems that the existing preparation period of the silica aerogel is long and a large amount of solvents are wasted can be solved.

The technical scheme of the invention is further described in detail below through a plurality of embodiments and with reference to the accompanying drawings. However, the examples are chosen to illustrate the invention only and are not intended to limit the scope of the invention.

Example 1

The invention is based on a method for continuously preparing silica aerogel by adopting a micro-channel mixing reaction device,

Referring to fig. 1, the microchannel mixing reaction device at least comprises a T-shaped micromixer, a microchannel I, and a microchannel II, wherein the T-shaped micromixer, the microchannel I, and the microchannel II are sequentially communicated, and the reaction raw materials are pumped into the T-shaped microchannel by a plurality of sample injection units to be mixed and subjected to continuous sol-gel conversion;

Continuously entering a micro-channel I to realize continuous sol-gel conversion, then entering a solvent replacement micro-channel II, carrying out first solvent replacement in a first solvent replacement cavity to obtain silica wet gel, and drying to obtain the hydrophilic silica aerogel.

Or, the wet gel obtained after the first solvent replacement enters a modification cavity through a micro-channel II, the modified wet gel is obtained under the action of a modifier, the wet gel enters a second solvent replacement cavity through a micro-channel III, the second solvent replacement is carried out, the modified wet gel is obtained, and finally the hydrophobic silica aerogel is obtained after drying.

The first solvent replacement cavity, the modification cavity and the second solvent replacement cavity comprise a solvent inlet and a solvent outlet, so that the dynamic working mode of the solvent can be realized in a working state.

Specifically, a PTFE capillary is selected as the micro-channel I; the length of the micro channel I is 10 cm-100 cm; the inner diameter of the micro-channel I is 0.1 mm-1 mm.

Specifically, the micro-channel II is a micro-tube wrapped by a PTFE micro-filtration membrane; the aperture of the micropores contained in the microfiltration membrane is 0.22-5 mu m; the inner diameter of the microtube is the same as the inner diameter of the micro-channel I; the length of the micro-channel II is 5 cm-100 cm.

Specifically, microchannel III or microchannel IV is an extension of microchannel II; the length of the micro-channel III or the micro-channel IV is 5 cm-100 cm.

Based on the microchannel mixing reaction device, the method for preparing the silica aerogel comprises the following specific steps:

1. Preparation of organosiloxane precursor solution: 15g TEOS was polycondensed in 13.3g ethanol and 2.5g water to form an organosiloxane precursor solution, the content of silicon in the organosiloxane being 6.6wt%.

2. Preparation of the catalyst: and adding a certain amount of ammonia water into ethanol, and stirring to form an alkaline catalyst, wherein the concentration of the ammonia water in the ethanol is 2mol/L.

3. Transformation of sol gel: the precursor solution and the alkaline catalyst are pumped into a sol-gel microchannel I through a T-shaped microchannel at the speed of 0.05mL/min, the inner diameter of the microchannel I is 1mm, the length of the microchannel I is 30cm, and the organosiloxane precursor is subjected to sol-gel conversion at 20 ℃ to obtain gel.

4. Continuously pumping the silica gel prepared in the step 3 into a solvent replacement micro-channel II, wherein the micro-channel II is a micro-tube wrapped by a micro-filtration membrane with the aperture of 0.22 mu m, the length of the micro-tube is 30cm, and the inner diameter of the micro-tube is 1mm; simultaneously pumping ethanol into the replacement chamber at the volume flow of 0.1mL/min for 2min, and pumping n-hexane for 1min at the same volume flow to obtain the silica wet gel.

5. And (3) carrying out airflow spray drying on the silica wet gel prepared in the step (4), wherein the drying temperature is 200 ℃, and obtaining the hydrophilic silica aerogel.

Referring to fig. 2, a sample of the hydrophilic silica aerogel prepared in this example is shown, which can be quickly soaked in water after being immersed in water.

Referring to fig. 3, a scanning electron microscope image of the hydrophilic silica aerogel prepared in this example shows that the hydrophilic silica aerogel prepared based on the micro-channels has the same three-dimensional network structure as the silica aerogel prepared by the conventional batch method, and the spherical silica element size is in nano-scale.

Referring to fig. 4, which is an optical microscopic image of the hydrophilic silica aerogel prepared in this example, it can be seen that the hydrophilic silica aerogel prepared based on the micro-channels has a size of 0.853mm and has obvious micro-channel size characteristics.

Example 2

Based on the microchannel mixing reaction device provided in embodiment 1, the embodiment provides a method for preparing silica aerogel, which comprises the following specific steps:

9g of TEOS is taken and condensed in 45.6g of methanol and 6g of water to form an organic siloxane precursor solution, wherein the content of silicon in the organic siloxane is 2wt%; and adding a certain amount of ammonia water into ethanol, and stirring to form an alkaline catalyst, wherein the concentration of the ammonia water in the ethanol is 10mol/L.

All micro-channels have an inner diameter of 0.5mm, wherein the length of the micro-channel I is 50cm; the solvent-substituted micro channel II is a microtube wrapped by a micro-filtration membrane with a pore diameter of 0.22 μm, and the length of the microtube is 50cm.

(1) The precursor solution is pumped into the sol-gel micro-channel through a T-shaped micro-mixer at the speed of 1mL/min and the alkaline catalyst at the speed of 2mL/min, and the sol-gel conversion is carried out at the temperature of 20 ℃.

(2) Pumping the gel prepared in the step (1) into a solvent replacement microchannel continuously, and pumping ethanol into a replacement chamber for 0.5min at the volume flow rate of 9mL/min at the same time; n-heptane was then pumped in at the same volumetric flow rate for 0.5min for displacement.

(3) And (3) carrying out airflow spray drying on the wet gel prepared in the step (2) to obtain the hydrophilic silica aerogel at 20 ℃.

Referring to fig. 5, which is a scanning electron microscope image of the hydrophilic silica aerogel prepared in this example, it can be seen that the hydrophilic silica aerogel prepared based on the micro channels has the same microstructure as in example 1.

Referring to FIG. 6, which is an optical microscopic view of the hydrophilic silica aerogel prepared in this example, it can be seen that the size of the hydrophilic silica aerogel prepared based on the micro channels is 0.417mm.

Example 3

Stirring 6.8g TMOS in 14gDMSO to form an organosiloxane precursor solution, wherein the content of silicon in the organosiloxane is 6wt%; and adding a certain amount of sodium hydroxide into ethanol, and stirring to form the alkaline catalyst, wherein the concentration of the sodium hydroxide in the ethanol is 1mol/L.

All micro-channels have an inner diameter of 0.6mm, wherein the length of the micro-channel I is 50cm; the solvent-substituted micro-channel II is a micro-tube wrapped by a micro-filtration membrane with a pore diameter of 0.45 μm, and the length of the micro-tube is 80cm.

(1) The precursor solution was pumped into the sol-gel microchannel through a T-type micromixer at a rate of 0.5mL/min and at a basic catalyst rate of 0.6mL/min, and subjected to sol-gel conversion at 40 ℃.

(2) The gel prepared in the step (1) is continuously pumped into a solvent replacement micro-channel, meanwhile, ethanol is pumped into a replacement chamber for replacement for 1min at the speed of 55mL/min, and then cyclohexane is pumped into the replacement chamber for replacement for 1min at the same volume flow rate.

(3) And (3) drying the wet gel prepared in the step (2) at normal pressure and at 20 ℃ to obtain the hydrophilic silica aerogel.

Example 4

13g TMOS was stirred in 10gDMF to form an organosiloxane precursor solution, the organosiloxane having a silicon content of 10.4wt%; a certain amount of sodium hydroxide is added into ethanol and stirred to form an alkaline catalyst, wherein the concentration of the sodium hydroxide in the ethanol is 6.87mol/L.

The inner diameters of all the micro-channels are 1mm, wherein the length of the micro-channel I is 100cm; the solvent-substituted micro channel II is a microtube wrapped by a micro-filtration membrane with a pore diameter of 0.45 μm, and the length of the microtube is 100cm.

(1) The precursor solution and the alkaline catalyst are pumped into the sol-gel micro-channel through a T-shaped micro-mixer at the speed of 10mL/min, and sol-gel conversion is carried out at the temperature of 60 ℃.

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

(3) And (3) carrying out supercritical drying on the wet gel prepared in the step (2) to obtain the hydrophilic silica aerogel.

Example 5

9g of TEOS, 6gDMDMS and 5.5gTMOS are taken, and are condensed in 26g of ethanol and 3.9g of water to form an organic siloxane precursor solution, wherein the silicon content of the organic siloxane is 7.2wt%; adding a certain amount of ammonia water into water, and stirring to form an alkaline catalyst, wherein the concentration of the ammonia water in the water is 5mol/L.

All micro-channels have an inner diameter of 0.8mm, wherein the length of the micro-channel I is 10cm; the solvent-substituted micro channel II is a microtube wrapped by a 5 μm aperture micro-filtration membrane, and is 5cm long.

(1) The precursor solution and the alkaline catalyst are pumped into the sol-gel micro-channel through a T-shaped micro-mixer at the speed of 0.05mL/min, and sol-gel conversion is carried out at 50 ℃.

(2) Continuing to pump the gel prepared in the step (1) into the solvent replacement micro-channel, and simultaneously pumping tertiary butanol into the replacement chamber for 0.25min at a speed of 5mL/min outside.

(3) Freezing the wet gel prepared in the step (2) at the temperature of-12 ℃ for 8 hours, and then putting the wet gel into a vacuum freeze dryer for freeze drying to obtain the hydrophilic silica aerogel.

Example 6

Polycondensing 10g of TEOS, 1.4gDMDMS in 6g of methanol and 1g of water to form an organosiloxane precursor solution, wherein the silicon content is 9.1wt%; weighing a certain amount of ammonia water, adding the ammonia water into ethanol, and stirring to form an alkaline catalyst, wherein the concentration of the ammonia water in the ethanol is 8mol/L.

The inner diameters of all the micro-channels are 1mm, wherein the length of the micro-channel I is 30cm; the solvent replacement micro-channel II, the modified micro-channel III and the solvent replacement micro-channel IV are micro-tubes wrapped by a micro-filtration membrane with a pore diameter of 5 mu m, wherein the length of the micro-channel II is 6cm, the length of the micro-channel III is 5cm, and the length of the micro-channel IV is 12cm.

(1) The precursor solution is pumped into a sol-gel microchannel I through a T-shaped micromixer at a speed of 0.3mL/min and a basic catalyst at a speed of 0.2mL/min, and sol-gel conversion is carried out at 20 ℃.

(2) And (3) continuing to pump the gel prepared in the step (1) into the solvent replacement micro-channel II, and simultaneously pumping methanol into the first solvent replacement chamber at the speed of 4mL/min for 1min outside.

(3) Pumping the wet gel prepared in the step (2) into a hydrophobic modification channel III continuously, and pumping TMCS into a modification cavity at the external part at the volume flow of 10mL/min for modification for 0.5min; and (3) continuously inputting the gel into a second solvent replacement cavity, and pumping methanol into the second solvent replacement cavity at a volume flow of 5mL/min for replacement for 1min, and replacing the methanol with n-hexane for 1min.

(4) And (3) carrying out spray drying on the wet gel prepared in the step (3), wherein the drying temperature is 100 ℃, and obtaining the hydrophobic silica aerogel.

Referring to fig. 7, a scanning electron microscope image of the hydrophobic silica aerogel prepared in this example shows that the hydrophobic silica aerogel prepared based on the micro channels has the same microstructure as the hydrophilic silica aerogel of example 1 and example 2.

Referring to fig. 8, a graph of nitrogen adsorption of the hydrophobic silica aerogel prepared in this example shows that the hydrophobic silica aerogel prepared based on the micro-channel has a nitrogen adsorption/desorption isotherm of IV-H1 type hysteresis loop, and the obtained silica aerogel is proved to be a spherical particle aggregate with uniform size, which is composed of mesopores between micropores (less than 2 nm) and macropores (more than 50 nm).

Referring to fig. 9, a graph of pore size distribution of micropores included in the hydrophobic silica aerogel prepared in this example shows that the average particle size of the hydrophobic silica aerogel prepared based on the micro channels is between 15nm and 20nm, thereby illustrating that the nano-scale porous silica aerogel material is successfully prepared in this example.

Referring to fig. 10, a TG graph of the hydrophobic silica aerogel prepared in this example shows that the hydrophobic silica aerogel prepared based on the micro-channels has a mass residual rate of 79.1% when heated to 900 ℃ and has good thermal stability.

Fig. 11 is a graph of a contact angle of the hydrophobic silica aerogel prepared in this example, and it can be seen from the graph that the hydrophobic silica aerogel prepared based on the micro-channels has a contact angle as high as 141.9 °, and has a good hydrophobic effect.

Example 7

Stirring 15g of TMOS in 1g of ethanol to form an organosiloxane precursor solution, wherein the content of silicon in the organosiloxane is 17.3wt%; and adding a certain amount of sodium hydroxide into ethanol, and stirring to form the alkaline catalyst, wherein the concentration of the sodium hydroxide in the ethanol is 2mol/L.

The inner diameters of all the micro-channels are 1mm, wherein the length of the micro-channel I is 50cm; the solvent replacement micro-channel II, the modified micro-channel III and the solvent replacement micro-channel IV are micro-tubes wrapped by a micro-filtration membrane with the aperture of 0.45 mu m, wherein the length of the micro-channel II is 50cm, the length of the micro-channel III is 50cm, and the length of the micro-channel IV is 100cm.

(3) The precursor solution was pumped into the sol-gel microchannel I at a rate of 2mL/min and the alkaline catalyst at a rate of 1.5mL/min through a T-type micromixer, and subjected to sol-gel conversion at 40 ℃.

(4) And (3) continuing to pump the gel prepared in the step (3) into the solvent replacement micro-channel II, and simultaneously pumping ethanol into the first solvent replacement cavity for 0.1min at the volume flow rate of 200 mL/min.

(5) And (3) continuously pumping the wet gel prepared in the step (4) into a hydrophobic modification channel III, simultaneously pumping the HDMS into a modification cavity at the external volume flow of 200mL/min, performing hydrophobic modification for 0.1min, continuously inputting the wet gel into a micro channel IV, and pumping tertiary butanol into a second solvent replacement cavity at the volume flow of 100mL/min for 0.2min.

(6) Freezing the wet gel prepared in the step (2) at the temperature of-12 ℃ for 8 hours, and then putting the wet gel into a vacuum freeze dryer for freeze drying to obtain the hydrophobic silica aerogel.

Fig. 12 is a graph of the contact angle of the hydrophobic silica aerogel prepared in this example, and it can be seen from the graph that the contact angle of the hydrophobic silica aerogel prepared based on the micro-channels is up to 125.8 °, and the hydrophobic effect is good.

Example 8

7.5g of TEOS and 3gMTMS are taken in 13.3gDMF g of water and 2.6g of water to form an organic siloxane precursor solution by polycondensation, wherein the silicon content is 6.2wt%; a certain amount of sodium hydroxide is weighed and added into water to be stirred to form an alkaline catalyst, and the concentration of the sodium hydroxide in the water is 15mol/L.

The inner diameters of all the micro-channels are 0.8mm, wherein the length of the micro-channel I is 30cm; the solvent replacement micro-channel II, the modified micro-channel III and the solvent replacement micro-channel IV are micro-tubes wrapped by a micro-filtration membrane with a pore diameter of 5 mu m, wherein the length of the micro-channel II is 60cm, the length of the micro-channel III is 30cm, and the length of the micro-channel IV is 90cm.

(3) The precursor solution and the alkaline catalyst are pumped into a sol-gel microchannel I through a T-shaped micromixer at the speed of 0.3mL/min, and sol-gel conversion is carried out at 50 ℃.

(4) And (3) continuing to pump the gel prepared in the step (3) into the solvent replacement micro-channel II, and simultaneously pumping methanol into the first solvent replacement cavity to replace the methanol for 0.5min at the volume flow rate of 60 mL/min.

(5) And (3) continuously pumping the wet gel prepared in the step (4) into a hydrophobic modification channel III, pumping HMDS into a modification cavity at the external volume flow rate of 6mL/min, hydrophobically modifying for 0.25min, inputting into a micro-channel IV, and pumping methanol into a second solvent replacement cavity at the volume flow rate of 60mL/min for 0.75min.

(6) And (3) carrying out supercritical drying on the wet gel prepared in the step (5) to obtain the hydrophobic silica aerogel.

Example 9

Taking 0.5g of TEOS and 20gTMOS to 0.5: 0.5gDMSO, and stirring to form an organosiloxane precursor solution, wherein the silicon content is 17.9wt%; a certain amount of strong ammonia water is weighed as an alkaline catalyst, and the concentration of the ammonia water is 13.3mol/L.

The inner diameters of all the micro-channels are 1mm, wherein the length of the micro-channel I is 100cm; the solvent replacement micro-channel II, the modified micro-channel III and the solvent replacement micro-channel IV are micro-tubes wrapped by a micro-filtration membrane with the aperture of 0.22 mu m, wherein the length of the micro-channel II is 100cm, the length of the micro-channel III is 100cm, and the length of the micro-channel IV is 100cm.

(3) The precursor solution and the alkaline catalyst are pumped into a sol-gel microchannel I through a T-shaped micromixer at a speed of 5mL/min, and sol-gel conversion is carried out at 60 ℃.

(4) And (3) continuing to pump the gel prepared in the step (3) into the solvent replacement micro-channel II, and simultaneously pumping methanol into the first solvent replacement cavity to replace the methanol for 0.1min at a volume flow rate of 40 mL/min.

(5) And (3) continuously pumping the wet gel prepared in the step (4) into a hydrophobic modification channel III, simultaneously pumping TMCS into a modification cavity at the external volume flow rate of 100mL/min, hydrophobically modifying for 0.1min, continuously inputting into a micro-channel IV, and pumping cyclohexane into a second solvent replacement cavity at the volume flow rate of 40mL/min for 0.1min.

(6) And (3) drying the wet gel prepared in the step (5) at normal pressure, and drying at 80 ℃ for 12 hours to obtain the hydrophobic silica aerogel.

Example 10

3gTMOS and 17gMTMS are taken in 0.5gDMF, and are condensed to form an organic siloxane precursor solution, wherein the silicon content is 20wt%; a certain amount of sodium hydroxide is weighed and added into water to be stirred to form an alkaline catalyst, and the concentration of the sodium hydroxide in the water is 4mol/L.

The inner diameters of all the micro-channels are 0.5mm, wherein the length of the micro-channel I is 85cm; the solvent replacement micro-channel II, the modified micro-channel III and the solvent replacement micro-channel IV are micro-tubes wrapped by a micro-filtration membrane with the aperture of 0.22 mu m, wherein the length of the micro-channel II is 20cm, the length of the micro-channel III is 30cm and the length of the micro-channel IV is 10cm.

(3) The precursor solution was pumped into the sol-gel microchannel I at a rate of 0.07mL/min and the alkaline catalyst at a rate of 0.03mL/min through a T-type micromixer, and sol-gel conversion was performed at 40 ℃.

(4) And (3) continuing to pump the gel prepared in the step (3) into the solvent replacement micro-channel II, and simultaneously pumping ethanol into the replacement chamber for 0.33min at a volume flow rate of 5 mL/min.

(5) And (3) continuously pumping the wet gel prepared in the step (4) into a hydrophobic modification channel III, simultaneously pumping HMDSO into a modification cavity at the external volume flow of 20mL/min, hydrophobically modifying for 0.5min, continuously inputting into a micro-channel IV, and pumping cyclohexane into a second solvent replacement cavity at the volume flow of 1mL/min for 0.2min.

(6) And (3) drying the wet gel prepared in the step (5) at normal pressure, and drying at 200 ℃ for 2 hours to obtain the hydrophobic silica aerogel.

Comparative example 1

Under the same conditions, the silica aerogel was prepared by conventional batch technology and used in comparative example 1, and the specific preparation process is as follows:

3. Transformation of sol gel: 1mL of precursor solution and 1mL of alkaline catalyst are poured into a glass bottle to be stirred and mixed, and the mixture is stood at 20 ℃ to wait for sol-gel conversion to obtain gel.

4. Replacing the silica gel prepared in the step 3 with 2mL of ethanol for 10 times, wherein each replacement is carried out for 30min; reuse 2

The silica wet gel is obtained by replacing the normal hexane for 2 times with 30min interval.

Referring to FIG. 13, which is an infrared chart of silica aerogel prepared by micro-channel technology and batch technology according to example 1 and comparative example 1 of the present invention, it can be seen that a strong and broad Si-O vibration peak at 1100cm ^-1 indicates that a large number of-Si-O-Si-groups are present in silica aerogel, the O-H vibration peak at 3200cm ^-1 indicates the presence of-OH groups in the aerogel, and the corresponding tensile and flexural vibrations at 2900cm ^-1 and 1200cm ^-1 are peaks of C-H bonds, respectively. In combination with the electron microscope photograph and the optical photograph analysis of example 1, it is apparent that the silica aerogel obtained by adopting the technical scheme of the invention has the same three-dimensional porous network structure and chemical bond composition as the silica prepared intermittently in the prior art.

Comparative example 2

Under the same conditions, the silica aerogel was prepared by conventional batch technology and used in comparative example 6, and the specific preparation process is as follows:

(1) 1.5ML of the precursor solution and 1mL of the alkaline catalyst were mixed in a glass bottle with stirring, and the mixture was left to stand at 20℃until sol-gel transition was performed.

(2) The gel prepared in step (1) was replaced with 20mL of methanol 6 times at intervals of 30min.

(3) Modifying the wet gel prepared in the step (2) with 20mLTMCS for 30min; then replaced 6 times with 25mL of methanol, 30min each time, and 1 time with 25mL of n-hexane.

(4) And (3) carrying out spray drying on the wet gel prepared in the step (5) at a drying temperature of 100 ℃ to obtain the hydrophobic silica aerogel.

Referring to fig. 14, the contact angle of the hydrophobic silica aerogel prepared in this comparative example is shown to be 138.5 °, and the hydrophobic effect is better; comparative example 6, having a hydrophobic silica aerogel prepared based on a micro-channel with a contact angle of 141.9 °, demonstrates that the silica aerogel prepared based on a micro-channel has the same hydrophobic effect as the silica aerogel prepared by a conventional batch method. In addition, the total volume of the solvent required for the solvent replacement of the comparative example is 118 times the volume of the wet gel, and the total time for the replacement is 360 minutes; comparative example 6 hydrophobic silica aerogel was prepared based on a microchannel wherein the total volume of solvent required for dynamic solvent displacement was 28 times the volume of wet gel and the total displacement time was 3min; the dynamic solvent replacement based on the micro-channel can greatly save the solvent, reduce the time required by the solvent replacement and obviously improve the solvent replacement efficiency.

Further, physical properties of examples and comparative examples were tested, including density, specific surface area, pore volume, contact angle, and thermal conductivity of the prepared silica aerogel.

By combining the characterization graphs (including electron microscope, optical photo, pore volume and the like) in the above examples with the data analysis results of table 1, it is known that the silica aerogel prepared based on the micro-channel has the same high specific surface area and pore volume and excellent heat resistance as the silica aerogel prepared by the conventional batch method, and the hydrophobically modified silica aerogel can achieve the same hydrophobic effect.

Further, by comparing the solvents used in the examples and comparative examples, it was found that solvent replacement in the microchannels can save a large amount of solvent, greatly reduce the time required for replacement, and significantly improve the solvent replacement efficiency.

Table 1 results of performance tests of examples and comparative examples

As can be seen from Table 1, the silica aerogel prepared based on the micro-channels has low thermal conductivity, extremely low density and extremely high specific surface area as compared with the silica aerogel prepared by the conventional batch method under the same conditions, thereby further demonstrating the feasibility of the micro-chemical process.

The above is only a preferred embodiment of the present invention, which is not to be construed as limiting the scope of the present invention, and various modifications and variations of the present invention will be apparent to those skilled in the art. Variations, modifications, substitutions, integration and parameter changes may be made to these embodiments by conventional means or may be made to achieve the same functionality within the spirit and principles of the present invention without departing from such principles and spirit of the invention.

Claims

1. A continuous preparation method for continuously preparing silica aerogel based on a microchannel technology comprises the steps of continuously inputting raw materials into a microchannel mixing reaction device, continuously performing sol-gel conversion and solvent replacement, drying to generate silica aerogel, and continuously outputting.

2. The continuous preparation method of silica aerogel based on the microchannel technology according to claim 1, wherein the microchannel mixing reaction device at least comprises a continuous sol-gel transition section and a first solvent replacement section;

The continuous sol-gel transition section is a T-shaped micro-channel and comprises a plurality of input ends, a T-shaped micro-mixer and a micro-channel I, wherein the input ends are arranged in parallel;

After the reaction raw materials are input to the input end, uniformly mixing the reaction raw materials in the T-shaped micro mixer, and then entering the micro channel I for continuous sol-gel reaction to obtain a sol-gel product;

And the sol-gel product enters the micro-channel II, and meanwhile, a replacement solvent is injected into the first solvent replacement cavity for solvent replacement, so that wet gel is obtained.

3. The continuous preparation method of silica aerogel based on the microchannel technology according to claim 2, wherein the organosiloxane precursor solution and the alkaline catalyst are respectively and uniformly mixed by the T-shaped micromixer through different input ends, and then pumped into the microchannel I, wherein the total volume flow rate of the pumping is 0.1 mL/min-20 mL/min;

The length of the micro-channel I is 10 cm-100 cm; the inner diameter is 0.1 mm-1 mm; preferably, the micro-channel I is a PTFE capillary;

The micro-channel II is a micro-tube wrapped by a micro-filtration membrane; the aperture of the micropores contained in the microfiltration membrane is 0.22-5 mu m; the inner diameter of the micro-tube is the same as the inner diameter of the micro-channel I; the length of the micro-channel II is 5 cm-100 cm; preferably, the material of the micro-channel II is PTFE;

The sol-gel reaction conditions include: the reaction temperature is 20-60 ℃;

the organosiloxane precursor solution comprises an organosiloxane monomer and an organic solvent; the content of silicon in the organic siloxane precursor solution is 2-20wt%;

the alkaline catalyst comprises one of ammonia water or sodium hydroxide solution; the solvent of the alkaline catalyst comprises one of ethanol and water, and the concentration of alkali in the alkaline catalyst is 1 mol/L-15 mol/L;

The organic siloxane monomer comprises any one or more than two of tetraethoxysilane, tetramethyl orthosilicate, methyltrimethoxysilane and dimethyl dimethoxy siloxane;

The organic solvent comprises any one or more than two of methanol, ethanol, dimethylformamide, dimethyl sulfoxide and water;

the replacement solvent is selected from any one or more than two of methanol, ethanol, tertiary butanol, n-hexane, n-heptane and cyclohexane;

The volume flow of the input or output of the displacement solvent is 0.1 mL/min-200 mL/min.

4. The continuous preparation method of silica aerogel based on the microchannel technology according to claim 2, wherein the microchannel mixing reaction device further comprises a modification section, the modification section comprises a microchannel III and a modification cavity, a microchannel IV and a second solvent replacement cavity;

The micro-channel III is arranged in the modification cavity and is connected with the first solvent replacement cavity;

The micro-channel IV is arranged in the second solvent replacement cavity and is connected with the modification cavity;

inputting a modifying agent into the modifying cavity, and carrying out surface modification after the wet gel enters the micro-channel III; then, the mixture is continuously introduced into the micro-channel IV, and the solvent replacement operation is repeated, so that the modified wet gel is obtained.

5. The continuous production method of silica aerogel according to claim 4, wherein the microchannel III and the microchannel IV are extension sections of the microchannel II, and have the same inner diameter;

Preferably, the length of the micro-channel III or the micro-channel IV is 5 cm-100 cm;

The replacement solvent adopts dynamic input or output of the first solvent replacement cavity and/or the second solvent replacement cavity;

the modifier is input into or output from the modification cavity in a dynamic in-out mode;

And/or the volume flow of the input or output of the replacement solvent and/or the modifier is 0.1 mL/min-200 mL/min.

6. The continuous production method of silica aerogel according to claim 4, wherein the substitution solvent is selected from any one or a combination of two or more of methanol, ethanol, t-butanol, n-hexane, n-heptane, cyclohexane;

the modifier is a hydrophobic modifier and is selected from any one or more than two of trimethylchlorosilane, hexamethyldisilazane and hexamethyldisiloxane.

7. The method for the continuous preparation of silica aerogel according to any of claims 1 to 6, characterized in that the drying comprises supercritical drying, freeze drying, atmospheric drying and/or air-flow spray drying;

The supercritical drying includes: replacing liquid components in the gel material with supercritical fluid in a supercritical state to obtain aerogel material, wherein the supercritical fluid comprises any one of supercritical CO ₂, supercritical methanol and supercritical ethanol; and/or the number of the groups of groups,

The freeze-drying comprises vacuum freeze-decompression drying; the vacuum freeze drying comprises the steps of freezing a gel material to below a freezing point, and sublimating a solvent under a higher vacuum to obtain an aerogel material; preferably, the method of freezing comprises: freezing in the freezing device and directly and rapidly vacuumizing in the drying chamber to freeze; preferably, the cold trap temperature of the vacuum freeze drying is-45 ℃ to-80 ℃ and the vacuum degree is less than 0.1kPa;

The normal pressure drying comprises the following steps: replacing the pore solution in the wet gel with one or more solvents with low surface tension, and evaporating the solvents at normal pressure to obtain an aerogel material; preferably, the temperature of the evaporation is 20-200 ℃;

the airflow type spray drying comprises the steps of fully mixing gel materials with natural air, and then evaporating and drying; the temperature of the natural air is 20-200 ℃.

8. Silica aerogel prepared by the continuous production method according to any one of claims 1 to 7; the density of the silica aerogel is 0.04g/cm ³～0.3g/cm³, the size is 0.1 mm-1 mm, the specific surface area is 500m ²/g～1200m²/g, and the thermal conductivity is 0.015W/mk-0.045W/mk.

9. A microchannel mixing reaction device for preparing the silica aerogel according to claim 8, which is characterized by at least comprising a continuous sol-gel transition section and a first solvent replacement section, wherein the continuous sol-gel transition section is a T-type microchannel, and comprises a plurality of input ends arranged in parallel, a T-type micromixer for mixing reaction raw materials and a microchannel I connected with the sample introduction unit; the first solvent replacement section comprises a micro-channel II and a first solvent replacement cavity which are connected, and the micro-channel II is arranged in the first solvent replacement cavity;

The micro-channel I is a PTFE capillary; the length of the micro-channel I is 10 cm-100 cm; the inner diameter of the micro-channel I is 0.1 mm-1 mm;

The micro-channel II is a micro-tube wrapped by a micro-filtration membrane; the aperture of the micropores contained in the microfiltration membrane is 0.22-5 mu m; the inner diameter of the micro-tube is the same as the inner diameter of the micro-channel I; the length of the micro-channel II is 5 cm-100 cm.

10. The microchannel mixing reactor of claim 9, further comprising a modification section and a second solvent replacement section; the modification section and the second solvent replacement section may be a plurality of repeating units to surface modify the wet gel material;

The modification section comprises a micro-channel III, a modification cavity, a micro-channel IV and a second solvent replacement cavity;

The micro-channel III and the micro-channel IV are extension sections of the micro-channel II; the length of the micro-channel III or the micro-channel IV is 5 cm-100 cm.