Aerogel material and method for its preparation

Abstract

The application provides an aerogel material and a preparation method thereof, and a second solvent, solvent replacement and separation of a gel material containing a first solvent are carried out by a solvent replacement-circulation process to obtain the aerogel material; the first solvent and the second solvent are compatible. The second solvent is used as the main solvent in the aerogel material, and other solvents in the wet gel material are removed by circulation of the second solvent between the gas-liquid two phases, so that the harsh high temperature and high pressure and the complex pretreatment process in the preparation process of the aerogel material are avoided, and the production cost of the aerogel material is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, specifically to an aerogel material and its preparation method. Background Technology

[0002] Aerogel materials possess a unique three-dimensional nanoporous structure, characterized by high porosity, high specific surface area, and ultra-low density. This structure endows aerogel materials with unique properties such as low thermal conductivity, low dielectric constant, low refractive index, and high acoustic impedance. Since the preparation of aerogels in 1931, aerogel materials have evolved from oxide systems to metal systems, polymer systems, and carbon systems. Their application forms have also gradually expanded from bulk and powder forms to composite materials, thin films, and fibers. Aerogel materials have demonstrated extremely high application value in fields such as thermal insulation, aerospace, intelligent thermal management, adsorption catalysis, biomedicine, and sound insulation and noise reduction, earning accolades such as "materials that change the world" and "a new state of matter."

[0003] Typically, existing aerogel preparation methods consist of two parts: precursor preparation and solvent removal (drying). Precursor preparation is a simple process and a common method for aerogel preparation. The core of drying technology lies in ensuring that the solvent in the gel is replaced by gas and that the gel skeleton does not collapse.

[0004] In principle, the solvent removal process from a gel necessarily involves a gas-liquid transition. This can be explained by the capillary force formula: Where, p r Let γ be the capillary force, r be the pore size, γ be the surface tension of the liquid, and θ be the contact angle between the liquid and the pore wall. It can be seen that the capillary force is positively correlated with the surface tension of the liquid and negatively correlated with the pore size. Since aerogels contain a large number of mesopores, the surface tension directly causes a huge capillary force to be generated during the transition from liquid to gas phase within the gel's pore structure, leading to the collapse of the gel material's skeletal structure.

[0005] Obviously, how to avoid or resist the influence of capillary force on the pore structure to avoid the collapse of the skeleton of the percolation material is the key to the successful preparation of aerogel. In the prior art, the drying method in the preparation of aerogel mainly adopts three technologies: supercritical drying technology, freeze drying technology and atmospheric drying technology, which realizes the avoidance or resistance to the influence of capillary force by adopting different solvent phase change routes. Supercritical drying and freeze drying technology is a common drying technology for aerogel preparation, and the aerogel material prepared has superior performance and less gel structure collapse. Atmospheric drying is a method of modifying the hydrophobicity of the precursor solution, and then obtaining the final aerogel structure through a certain temperature rising system without special equipment, which can be completed by ordinary heating equipment. However, this drying method has high requirements for the material itself and needs complex pretreatment steps, so it can only be applied to specific gel materials and is less used in practice.

[0006] Further, supercritical drying is to convert the drying medium into a supercritical state at high temperature and high pressure, reduce the surface tension to zero, and prevent the shrinkage and collapse of aerogel. For example, Chinese invention patent CN115504451A discloses a high specific surface area carbon aerogel and a preparation method thereof. By the method of supercritical drying, a phenolic resin aerogel is obtained, and finally a carbon aerogel is obtained by carbonization. The collapse of the gel structure is inhibited by the way of supercritical drying. However, supercritical carbon dioxide has a serious corrosive effect on general metal materials. The whole preparation process is complex and requires harsh conditions for equipment. Therefore, the method of supercritical drying requires special drying equipment, has low drying efficiency, requires large investment in equipment and site, results in high cost, and cannot be widely used.

[0007] Freeze drying is a drying technology in which the solvent and the gel are frozen at low temperature and low pressure, and then subjected to vacuum sublimation treatment. For example, Chinese invention patent CN107057107A discloses a method for preparing cellulose aerogel by freeze drying. However, compared with the aerogel prepared by the supercritical drying method, the quality of the aerogel obtained by freeze drying has certain gap. Because the freezing of the liquid in the gel inside is a change from liquid to solid in the process of freeze drying, some volume changes occur, and there is a tendency of crystal nucleus formation and solvent crystal growth, which will cause damage to the three-dimensional network structure of the aerogel. On the one hand, it will lead to the formation of very large pores in the aerogel, and on the other hand, the prepared aerogel is often difficult to preserve the original gel network structure, resulting in deformation of the aerogel.

[0008] In summary, in the prior art, the drying methods used in the prior art to prepare aerogel have the disadvantages of high cost and difficulty in popularization and use, or the problems of gel deformation or collapse in the drying process, or the problems of selectivity to gel materials and inability to be used universally. Therefore, a drying method for aerogel with universality, simple process, flexible operation and low cost is developed. SUMMARY

[0009] Therefore, based on the problems of the prior art, the present application provides an aerogel material and a preparation method thereof, which adopts an aerogel drying method different from the prior art, and through adjusting the liquefaction and gasification mode in the solvent circulation process, an extremely low capillary force is generated in the drying process, so that various drying modes can be flexibly adjusted by adjusting the equipment investment, the cost is low, and the applicability is also wide.

[0010] To achieve the above-mentioned purpose, the present application provides a preparation method of an aerogel material, which provides a wet gel containing a first solvent and a second solvent, and through a solvent displacement-circulation process, the second solvent and the first solvent are displaced and separated; the first solvent and the second solvent are compatible.

[0011] Preferably, the solvent displacement-circulation process includes circulating the second solvent between the gas-liquid two states by controlling the pressure or temperature to obtain the aerogel material; the first solvent is in contact with the liquid second solvent and carries the first solvent away from the gel material; the second solvent is converted from the liquid state to the gaseous state, so that the gel material is converted into the aerogel material.

[0012] Preferably, the solvent displacement-circulation process is a quasi-Carnot cycle, including four processes of compression-dissolution-expansion-separation; in the solvent displacement-circulation process, the second solvent is circulated in two states through the gaseous state and the liquid state.

[0013] Preferably, the compression process in the solvent displacement-circulation process includes liquefying the second solvent by pressurizing or cooling; the dissolution process in the solvent displacement-circulation process includes the liquid second solvent being in contact with the gel material and dissolving the first solvent therein; the expansion process in the solvent displacement-circulation process includes the liquid second solvent being converted from the liquid state to the gaseous state by heating or decompressing; and the separation process in the solvent displacement-circulation process is the separation of the second solvent from the first solvent.

[0014] Preferably, in the expansion process in the solvent displacement-circulation process, the heating or decompressing is gradient decompressing, or gradient heating, so that the second solvent is converted from the liquid state to the gaseous state to obtain the aerogel material.

[0015] Preferably, the second solvent is C m H n F x Cl y Br z Solvent, wherein the relationship between the atomic numbers m, n, x, y, z is 2m+2=n+x+y+z, and m≤2.

[0016] As a preferred embodiment, the second solvent includes, but is not limited to, CCl3F, CHClF2, C2H2F4, CHF5, etc.

[0017] Specifically, C m H n F x Cl y Br z The compression process of the solvent is to liquefy the gaseous C m H n F x Cl y Br z under pressure or cooling; the dissolving process is to dissolve the solvent in the gel material; the expansion process is to change the liquid C m H n F x Cl y Br z from liquid to gas by heating or decompression; and the separation process is to separate the gaseous C m H n F x Cl y Br z from the liquid solvent. m H n F x Cl y Br z from the liquid solvent.

[0018] Preferably, the C m H n F x Cl y Br z solvent is compressed at a pressure of 3-5 MPa and cooled to -60°C, and is expanded by decompression to atmospheric pressure or by heating to room temperature.

[0019] Preferably, the C m H n F x Cl y Br z solvent is dissolved by keeping the C m H n F x Cl y Br z solvent in liquid state under low-temperature or high-pressure environment, and is contacted with the gel material; the low-temperature environment is -20 to -60°C, and the high-pressure environment is 3-5 MPa.

[0020] Preferably, the C m H n F x Cl yBr z C m H n F x Cl y Br z The temperature is room temperature and the pressure is atmospheric pressure.

[0021] The first solvent is a polar or non-polar solvent compatible with the second solvent.

[0022] The gel material can be obtained by the prior art technology for preparing a gel material precursor. The solvent of the liquid contained in the obtained gel material is determined by the preparation process. Before the solvent replacement-circulation process, the solvent of the liquid in the gel material needs to be replaced by the solvent replacement method to obtain a gel material containing a solvent compatible with the second solvent. Preferably, the first solvent selected by the present application includes but is not limited to one or a mixture of two or more of methanol, ethanol, n-hexane, cyclohexane, acetone, carbon tetrachloride, dichloromethane.

[0023] As a preferred embodiment, the technical solution of the present application further includes a solvent replacement step; the solvent replacement step includes: replacing the solvent of the gel material containing a solvent incompatible with the second solvent by the solvent replacement method with the first solvent to obtain the gel material containing the first solvent.

[0024] Preferably, the gel material includes one or a mixture of two or more of polyamide gel, polyurethane gel, polyester gel, cellulose gel, polyether gel, carbon material gel, and silicon oxide gel.

[0025] Preferably, the morphology of the gel material can be powder, fiber, film, block, and derived morphology of the above morphology.

[0026] The aerogel obtained by the technical solution of the present application can maintain the morphology of the original gel material. The aerogel obtained by the above preparation method includes one or a mixture of two or more of polyamide aerogel, polyurethane aerogel, polyester aerogel, cellulose aerogel, polyether aerogel, carbon material aerogel, and silicon oxide aerogel. The morphology of the aerogel material can be powder, fiber, film, block, and derived morphology of the above morphology.

[0027] Further, the aerogel obtained by the technical solution of the present application is a porous material, the pore structure is composed of micropores with a pore size ≤2 nm and / or mesopores with a pore size of 2-50 nm and / or macropores with a pore size ≥50 nm; the porosity is 60%-99%, and the specific surface area is 10-2000 m 2 / g.

[0028] Mechanism: the present application utilizes C m H n F x Cl y Br z The low boiling point characteristics of the solvent, which is mostly gaseous at room temperature, can be easily liquefied by pressurization or cooling, and by utilizing its good compatibility with a large amount of solvent, after dissolving the solvent, it can be separated from the solvent to be removed by heating or decompression.

[0029] C m H n F x Cl y Br z The low-temperature environment required for the solvent to maintain a liquid state is not harsh, and can remain stable in a liquid state at normal pressure and low temperature environment, so a quasi-Carnot cycle process four-step cycle can be used to regulate the temperature and pressure of the solvent to circulate between gas and liquid, continuously removing the solvent from the gel material, and because of its extremely low surface tension, the capillary force generated when the solvent gasifies and leaves the gel material is extremely low, which will not cause the collapse of the gel skeleton.

[0030] Compared with the traditional drying method, this method can be considered as a new type of aerogel drying method different from the three drying methods of supercritical drying technology, freeze drying technology and normal pressure drying technology in the prior art. By adjusting the liquefaction and gasification mode in the solvent circulation process, various drying methods can be flexibly adjusted, and the drying conditions are relatively mild, the cost is much lower than the existing drying methods, especially the supercritical drying technology and freeze drying technology, and the method has universality and is suitable for various gel materials. It can be used for the preparation of aerogels of various materials and morphologies, and has excellent universality.

[0031] The beneficial technical effects obtained by the present application are:

[0032] 1. The second solvent (C m H n F x Cl y Br z Solvent) is used as the main solvent in the aerogel material to be dried, and C m H n F x Cl y Br z Solvent is circulated between gas and liquid to remove other solvents in the wet gel material, so that the harsh high temperature and high pressure and complex pretreatment process in the preparation of aerogel materials are avoided, and the production cost of aerogel materials is effectively reduced.

[0033] 2. The present application utilizes Cm H n F x Cl y Br z As a solvent, due to its extremely low surface tension, the capillary force generated when it vaporizes out of the gel material is extremely low, thereby avoiding the occurrence of collapse of the gel skeleton.

[0034] 3. By using the technical scheme of the present application, the C m H n F x Cl y Br z Quasi-Carnot cycle is carried out between gas and liquid, and the solvent in the gel material contacts and is taken away from the gel structure with liquid C m H n F x Cl y Br z After the solvent is completely taken away, the gel material is converted into aerogel material at normal temperature and pressure, ensuring that the aerogel material can maintain the original morphology of the original gel material and will not deform and other problems.

[0035] 4. By using the technical scheme of the present application, the gel material that can be used is very extensive, and the preparation of aerogel of various materials and morphologies is very universal.

[0036] 5. Compared with the prior art, by using the technical scheme of the present application, the liquefaction and gasification mode in the solvent circulation process can be flexibly adjusted to realize various drying modes, the drying conditions are relatively mild, and the present application can be combined with the equipment in the prior art, without the need for special drying equipment, thereby greatly saving the equipment cost, the drying efficiency is high, and the production cost is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 SEM image of the polyamide aerogel block prepared in Example 1 of the present application.

[0038] Figure 2 Photo of the polyurethane aerogel block prepared in Example 2 of the present application.

[0039] Figure 3 SEM image of the polybutylene terephthalate aerogel film prepared in Example 3 of the present application.

[0040] Figure 4 Photo of the polybutylene terephthalate aerogel fiber prepared in Example 4 of the present application.

[0041] Figure 5 Photo of the cellulose aerogel powder prepared in Example 5 of the present application.

[0042] Figure 6 The photograph of the polydimethylsiloxane aerogel block prepared in Example 8 of the present application.

[0043] Figure 7 The SEM image of the poly(p-phenyleneterephthalamide) aerogel block prepared in Comparative Example 1 of the present application.

[0044] Figure 8 The schematic diagram of the device structure for preparing aerogel adopted in Example 1 of the present application. DETAILED DESCRIPTION

[0045] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application.

[0046] The present application provides a preparation method of aerogel material. Through a solvent replacement-circulation process, a second solvent which is soluble with a first solvent contained in the gel material is selected to replace and separate the first solvent, so as to realize drying and obtain the aerogel material. The second solvent is selected as the gas solvent in the aerogel material.

[0047] The solvent replacement-circulation process includes forming a circulation system by controlling pressure or temperature to make the second solvent circulate between gas and liquid states; the first solvent contacts the liquid second solvent and carries the first solvent away from the gel material; the gel material is converted into the aerogel material; the first solvent is separated after the second solvent is gasified, and the second solvent returns to the circulation system.

[0048] In some preferred embodiments, the replacement-circulation process is carried out in a closed reaction container. The gel material is placed in the reaction container, the first solvent in the gel material is replaced by the liquid second solvent, the mixed solvent after replacement is discharged to obtain the gel material containing only the second solvent; the second solvent in the reaction container is converted from liquid state to gas state by a pressure / temperature control device (a pressurizing pump or a refrigerator) to obtain the aerogel material. Preferably, the conversion of the second solvent from liquid state to gas state adopts a gradient heating or gradient pressurizing method. The present application does not limit the rate and holding time of the gradient heating or gradient pressurizing.

[0049] Preferably, the second solvent and the first solvent are separated, the second solvent is recycled and utilized in the reaction container, and the first solvent is discharged.

[0050] In some preferred embodiments, the second solvent is C m H n F x Cl y Brz The solvent, wherein the relationship between the atomic numbers m, n, x, y, z is 2m+2=n+x+y+z, wherein m≤2.

[0051] In some preferred embodiments, the first solvent includes, but is not limited to, one or more than two mixed solvents of methanol, ethanol, n-hexane, cyclohexane, acetone, carbon tetrachloride, dichloromethane.

[0052] In some preferred embodiments, the solvent displacement-circulation process is a quasi-Carnot cycle, including four processes of compression-dissolution-expansion-separation, in which C m H n F x Cl y Br z The solvent presents a gas-liquid two-phase cycle.

[0053] In some preferred embodiments, C m H n F x Cl y Br z The compression process of the solvent is to liquefy the gaseous C m H n F x Cl y Br z by pressurization or cooling; the dissolution process is to dissolve the solvent in the gel material by contacting the liquid C m H n F x Cl y Br z ; the expansion process is to change the liquid C m H n F x Cl y Br z from liquid to gas by heating or decompression; and the separation process is to separate the gaseous C m H n F x Cl y Br z from the liquid solvent.

[0054] In some preferred embodiments, the morphology of the gel material used is powder, fiber, film, block, and derived morphologies of the above morphologies, and since the morphology of aerogel remains unchanged before and after drying, the morphology of the obtained aerogel material is also powder, fiber, film, block, and derived morphologies of the above morphologies.

[0055] In some preferred embodiments, the aerogel material prepared comprises: two or more of polyamide aerogel, polyurethane aerogel, polyester aerogel, cellulose aerogel, polyether aerogel, carbon material aerogel, and silica aerogel.

[0056] In some preferred embodiments, the aerogel material prepared is a porous structure material, having a porosity of 60% to 99% and a specific surface area of 10 to 2000 m 2 / g.

[0057] The technical solutions of the present application are further described in detail below through specific examples.

[0058] Example 1

[0059] The present example provides a preparation method of a polyamide aerogel block, and the specific steps include:

[0060] (1) Preparation of a precursor:

[0061] The terephthaloyl chloride, p-phenylenediamine and m-phenyl triamine are mixed in a molar ratio of 1:0.95:0.05 in DMSO, and then polymerized by heating to obtain a poly-p-phenyleneterephthalamide DMSO gel block. Preferably, the above gel block can be obtained by using the gel polymerization method of the prior art.

[0062] (2) Solvent replacement: the poly-p-phenyleneterephthalamide DMSO gel block prepared in step (1) is subjected to solvent replacement with ethanol as the solvent. Specifically, the gel material is soaked in ethanol, so that the DMSO solvent inside the gel material is removed, and the ethanol solvent enters the gel material. After multiple soaking, the DMSO in the poly-p-phenyleneterephthalamide DMSO gel block is completely replaced by ethanol, and a poly-p-phenyleneterephthalamide ethanol gel block is obtained.

[0063] (3) Preparation of aerogel and solvent separation:

[0064] Referring to Figure 8 , the present example uses a circulation system composed of a replacement kettle and a separation kettle connected in series, and is carried out in a closed replacement kettle. A pressurized pump is used to pressurize CCl3F to 5 MPa to liquefy it, and the pressure is maintained after liquefaction. The poly-p-phenyleneterephthalamide ethanol gel block prepared in step (1) is immersed in the liquefied CCl3F for solvent replacement, and at the same time, the pressure in the kettle is maintained at 5 MPa, and CCl3F is continuously injected into the kettle. The mixed solvent of CCl3F and ethanol is discharged and input into the separation kettle.

[0065] After the ethanol in the gel block is completely replaced by CCl3F, and the ethanol in the displacement tank is completely discharged into the separation tank, the pressure in the displacement tank is cycled from 4 MPa, 2 MPa to atmospheric pressure, and the CCl3F is gasified and expanded to obtain a poly-p-phenyleneterephthalamide aerogel block.

[0066] In the separation tank, CCl3F and ethanol are separated, ethanol is discharged through the separation tank, and CCl3F is returned to the displacement tank through the circulating pump for reuse.

[0067] Referring to Figure 1 The SEM image of the poly-p-phenyleneterephthalamide (or polyamide) aerogel block prepared in this embodiment is shown in the figure. As can be seen from the figure, the aerogel prepared by this method has a porous structure.

[0068] Example 2

[0069] This embodiment uses polyurethane methanol gel as raw material to provide a preparation method of polyurethane aerogel block.

[0070] (1) Preparation of precursor: aromatic polyurethane DMSO gel block is prepared by polymerization in DMSO solvent using toluene diisocyanate, polyoxypropylene glycol, and dimethylol propionic acid as monomers with a molar ratio of 0.95:1:0.05.

[0071] (2) Solvent replacement: the aromatic polyurethane DMSO gel block prepared in step (1) is immersed in methanol, and the DMSO in the gel block is replaced by methanol through solvent replacement to obtain a polyurethane methanol gel block.

[0072] (3) Preparation of aerogel and separation of solvent:

[0073] Referring to Figure 8 In this embodiment, a circulation system composed of a displacement tank and a separation tank connected in series is used. In the closed displacement tank, the polyurethane methanol gel block is immersed in liquid CCl3F to replace the methanol in the gel block with CCl3F. At the same time, the temperature in the tank is kept at -40°C, and CCl3F is injected into the tank to make CCl3F and methanol fully contact and complete the replacement. The mixed solvent of CCl3F and methanol after replacement is squeezed out by the continuously input CCl3F and input into the separation tank.

[0074] After the methanol in the displacement tank is completely replaced by CCl3F, i.e. the methanol is completely discharged into the separation tank, the temperature in the displacement tank is gradually increased to -40°C, -20°C, 0°C, and 20°C, respectively, to make the CCl3F gasified and expanded to obtain a poly-p-phenyleneterephthalamide aerogel block.

[0075] The mixed solvent of CCl3F and methanol is separated in the separation kettle, the methanol is discharged from the separation kettle, and the CCl3F is returned to the displacement kettle through the circulating pump for reuse.

[0076] Figure 2 The photograph of the polybutylene terephthalate aerogel bulk is shown in the figure, and it can be seen from the figure that the aerogel prepared by the embodiment can maintain the complete bulk structure.

[0077] Example 3

[0078] The embodiment takes polybutylene terephthalate as a raw material, and provides a preparation method of an aerogel film.

[0079] (1) The polybutylene terephthalate NMP gel film is prepared by coating the mixed solution of polybutylene terephthalate NMP and crosslinking agent. Preferably, the above gel film can be obtained by using the gel polymerization method of the prior art.

[0080] (2) Solvent displacement: The polybutylene terephthalate NMP gel film is immersed in n-hexane, and the NMP in the polybutylene terephthalate NMP gel film is replaced by n-hexane through solvent displacement to obtain a polybutylene terephthalate n-hexane gel film.

[0081] (2) Preparation of aerogel and solvent separation:

[0082] The embodiment selects the circulation system of Example 1.

[0083] In the displacement kettle, the refrigerating machine is used to cool CHClF2 to -60°C to liquefy it, and then maintain the temperature. The polybutylene terephthalate n-hexane gel film is immersed in the liquid CHClF2, the temperature in the displacement kettle is maintained at -60°C, and CHClF2 is continuously injected to make CHClF2 and n-hexane fully contact and replace each other. At the same time, the mixed solvent of the replaced CHClF2 and n-hexane enters the separation kettle.

[0084] After the n-hexane in the displacement kettle is completely discharged, the CHClF2 in the kettle is subjected to gradient temperature rise, and successively passes through -40°C, -20°C, 0°C and 20°C to make the CHClF2 gasify and expand to obtain a polybutylene terephthalate aerogel film.

[0085] The n-hexane and CHClF2 in the separation kettle are separated, the CHClF2 returns to the displacement kettle, and the n-hexane is discharged.

[0086] Figure 3The SEM image of the polybutylene terephthalate aerogel film prepared in this embodiment is shown in the figure. As can be seen from the figure, the obtained aerogel film material is a layered and porous aerogel structure formed by the lapping of nanosheet structures, and can maintain the original film morphology of the polybutylene terephthalate NMP gel film.

[0087] Example 4

[0088] This embodiment provides a preparation method of aerogel fibers using polybutylene terephthalate as a raw material.

[0089] (1) Preparation of precursor: polybutylene terephthalate NMP gel fibers are prepared using polybutylene terephthalate.

[0090] (2) Solvent replacement: NMP in the polybutylene terephthalate NMP gel fibers is replaced with n-hexane by solvent replacement to obtain polybutylene terephthalate n-hexane gel fibers.

[0091] (3) Preparation of aerogel and separation of solvent:

[0092] This embodiment uses the circulation system of Example 1.

[0093] A refrigeration machine is used to cool C2H2F4 in the replacement kettle to -60°C to liquefy C2H2F4, and the temperature is maintained after liquefaction. The polybutylene terephthalate n-hexane gel fibers are immersed in C2H2F4, so that C2H2F4 fully contacts the n-hexane in the gel fibers. The temperature in the kettle is maintained at -60°C, and C2H2F4 is continuously input to make C2H2F4 and n-hexane excluded to the separation kettle.

[0094] The C2H2F4 in the kettle is subjected to gradient warming, successively passing through -40°C, -20°C, 0°C, and 20°C, so that C2H2F4 is gasified and expanded to obtain polybutylene terephthalate aerogel fibers.

[0095] The n-hexane and C2H2F4 are separated, and the C2H2F4 is returned to the replacement kettle, and the n-hexane is discharged.

[0096] Reference Figure 4 The photo of the polybutylene terephthalate aerogel fibers prepared in this embodiment is shown in the figure. As can be seen from the figure, the obtained aerogel fibers are continuous fiber structures, and the fiber structure of the polybutylene terephthalate NMP gel fibers can be maintained by the scheme of this embodiment.

[0097] Example 5

[0098] This embodiment provides a preparation method of cellulose aerogel powder, and the specific steps include:

[0099] (1) α cellulose is dissolved in copper ammonia Cu(NH3)4(OH)2 solution to make a 5% concentration, and acetone is added dropwise until a gel is formed, then the gel is stirred and dispersed, and filtered to obtain cellulose acetone gel powder. Preferably, the above gel powder can be obtained by using the gel polymerization method of the prior art.

[0100] (2) Preparation of aerogel and solvent separation:

[0101] The circulation system of Example 1 is selected for this example.

[0102] A refrigerator is used to cool C2H2F4 in the displacement tank to -60°C to liquefy C2H2F4, and the temperature is maintained after liquefaction. The cellulose acetone gel is immersed in C2H2F4 to make C2H2F4 fully contact with acetone in the cellulose acetone gel. The temperature in the tank is maintained at -60°C, and C2H2F4 is continuously input to make C2H2F4 and acetone be excluded to the separation tank.

[0103] The C2H2F4 in the tank is subjected to gradient warming, and the gel powder is gasified and expanded in turn through -40°C, -20°C, 0°C, and 20°C environment to obtain cellulose aerogel powder.

[0104] The acetone and C2H2F4 are separated, and the C2H2F4 is returned to the displacement tank, and the acetone is discharged.

[0105] Referring to Figure 5 The cellulose aerogel powder prepared in this example is shown in the photo. As can be seen from the photo, the aerogel powder has good powder morphology and dispersity.

[0106] Example 6

[0107] This example uses polyethylene glycol hydrogel as raw material to provide a preparation method of aerogel block, and the specific steps include:

[0108] (1) Solvent displacement: polyethylene glycol is used to prepare polyethylene glycol hydrogel block, and solvent displacement is used to prepare polyethylene glycol tetrachloride block; preferably, the above gel block can be obtained by using the gel polymerization method of the prior art.

[0109] (2) Preparation of aerogel and solvent separation:

[0110] The circulation system of Example 1 is selected for this example.

[0111] The C2H2F4 in the displacement kettle is cooled to -60℃ by a refrigerator to liquefy the C2H2F4, the temperature is maintained after liquefaction, and the polyethylene glycol tetrachloromethane block is immersed in the C2H2F4 to make the C2H2F4 fully contact with the tetrachloromethane in the polyethylene glycol tetrachloromethane block, the temperature in the kettle is maintained at -60℃, and the C2H2F4 is continuously input to make the C2H2F4 and the tetrachloromethane be discharged into the separation kettle.

[0112] The C2H2F4 in the kettle is gradiently warmed to make the C2H2F4 gasify and expand in sequence through -40℃, -20℃, 0℃ and 20℃ environments to obtain the polyethylene glycol aerogel block.

[0113] The acetone and the C2H2F4 are separated, the C2H2F4 is returned to the displacement kettle, and the tetrachloromethane is discharged.

[0114] Example 7

[0115] This example takes graphene hydrogel as raw material to provide a preparation method of graphene aerogel block, and the specific steps include:

[0116] (1) Solvent displacement: graphene oxide is dispersed in water, ascorbic acid is added dropwise to gelate to obtain graphene hydrogel; the graphene hydrogel is immersed in dichloromethane to be graphene dichloromethane gel block through solvent displacement.

[0117] (2) Preparation of aerogel and solvent separation:

[0118] This example selects the circulation system of Example 1.

[0119] The C2H2F4 in the displacement kettle is cooled to -60℃ by a refrigerator to liquefy the C2H2F4, the temperature is maintained after liquefaction, and the graphene dichloromethane gel block is immersed in the C2H2F4 to make the C2H2F4 fully contact with the tetrachloromethane in the graphene dichloromethane gel block, the temperature in the kettle is maintained at -60℃, and the C2H2F4 is continuously input to make the C2H2F4 and the dichloromethane be discharged into the separation kettle.

[0120] The C2H2F4 in the kettle is gradiently warmed to make it gasify and expand in sequence through -40℃, -20℃, 0℃ and 20℃ environments, the dichloromethane and the C2H2F4 are separated, the C2H2F4 is returned to the circulation system, and the graphene aerogel block is obtained.

[0121] The dichloromethane and the C2H2F4 are separated, the C2H2F4 is returned to the displacement kettle, and the dichloromethane is discharged.

[0122] Example 8

[0123] This embodiment takes polydimethylsiloxane hydrogel (Xianfeng Nanometer Co., Ltd., GEL300) as raw material to provide a preparation method of polydimethylsiloxane gel block, and the specific steps include:

[0124] (1) solvent replacement: the solvent of polydimethylsiloxane hydrogel is replaced by polydimethylsiloxane ethanol gel block;

[0125] (2) preparation of aerogel and solvent separation:

[0126] This embodiment selects the circulation system of Example 1.

[0127] In a closed replacement kettle, a pressurized pump is used to pressurize CHF5 to 5 MPa to liquefy it, and the pressure is maintained after liquefaction. The polydimethylsiloxane ethanol gel block prepared in step (1) is immersed in liquefied CCl3F for solvent replacement, and at the same time, the pressure in the kettle is maintained at 5 MPa, and CHF5 is continuously injected into the kettle. CHF5 and ethanol mixed solvent are discharged and input into a separation kettle.

[0128] After the ethanol in the gel block is completely replaced by CHF5 and the ethanol in the replacement kettle is completely discharged into the separation kettle, the replacement kettle undergoes pressure cycles of 4 MPa, 2 MPa and atmospheric pressure in sequence, and CCl3F gasifies and expands to obtain a polydimethylsiloxane aerogel block.

[0129] In the separation kettle, CCl3F and ethanol are separated, ethanol is discharged through the separation kettle, and CCl3F is returned to the replacement kettle through a circulating pump for reuse.

[0130] Reference Figure 6 The photograph of the polydimethylsiloxane aerogel block prepared in this embodiment shows that the obtained aerogel material maintains a block morphology.

[0131] Comparative Example 1

[0132] This comparative example uses the poly-p-phenyleneterephthalamide DMSO gel block provided in Example 1 to dry by the supercritical drying method in the prior art.

[0133] After mixing p-phenyleneterephthalamide, p-phenylenediamine and m-phenyl triamine in a ratio of 1:0.95:0.05 in DMSO and heating to polymerize to form a poly-p-phenyleneterephthalamide DMSO gel block, solvent replacement is performed to obtain a poly-p-phenyleneterephthalamide ethanol gel block.

[0134] The poly-p-phenyleneterephthalamide ethanol gel block is dried by a supercritical carbon dioxide drying machine to obtain a poly-p-phenyleneterephthalamide aerogel block.

[0135] ReferenceFigure 7 The figure shows the poly(p-phenylene terephthalamide) aerogel block obtained by supercritical drying in this comparative example. As can be seen from the figure, the aerogel blocks obtained in Example 1 and this comparative example have similar structures, both being network structures constructed from nanofibers. The test data shows that the properties of the two aerogels are almost identical, indicating that the method of the examples is effective.

[0136] Comparative Example 2

[0137] The only difference between this comparative example and Example 2 is that in step (3) solvent separation, a compressor is used to pressurize CCl3F to liquefy it and then keep it at -40°C to impregnate the polyurethane methanol gel block. CCl3F is circulated and heated directly to 20°C to vaporize and expand CCl3F, thus obtaining poly(p-phenylene terephthalamide) aerogel block.

[0138] The aerogel block ruptured after vaporization and expansion in CCl3F, resulting in a broken aerogel block.

[0139] Clearly, the comparison between this comparative example and Example 2 shows that gradient heating can prevent the gas from expanding rapidly, which is beneficial from the perspective of production safety. On the other hand, it can also prevent the gel from breaking due to the rapid expansion of the gas.

[0140] The specific surface area, average pore size, and porosity of the aerogels prepared in Examples 1-8 were tested. BET pore structure analysis was used to analyze the specific surface area and average pore size of the aerogel materials, and mercury porosimetry was used to analyze the porosity of the materials.

[0141] Table 1. Performance test results of the aerogels prepared in the examples.

[0142] Specific surface area m 2 / g]] Average pore diameter nm Porosity % Example 1 220 13 95 Example 2 190 18 94 Example 3 310 10 93 Example 4 330 9 92 Example 5 320 10 93 Example 6 180 21 95 Example 7 260 14 96 Example 8 960 4 93

[0143] pass Figures 1-6 Analysis of the results in Table 1 shows that the aerogels prepared in Examples 1-8 have a porous structure. The internal pore structure consists of micropores with a pore size of less than 2 nm, mesopores with a pore size of 2-50 nm, and macropores with a pore size of more than 50 nm, with an average pore size between 4 and 21 nm. The aerogel material obtained through the above technical solution has a porous structure, high porosity, and excellent skeletal structural stability, and can maintain the original morphology of the wet gel without deformation or collapse.

[0144] The embodiments given in this invention do not include the range of practically applicable gel materials, but can be expanded to include various gel materials that can be selected in the prior art. The pore size of the obtained aerogel material can be controlled according to the selected gel material, and the porosity of the obtained aerogel material can be increased to 60% to 99%, and the specific surface area can be increased by 10 to 2000 m².2 / g.

[0145] Especially, the technical scheme of the present application is widely applied to dry wet gels, can be applied to various types of gel materials, has high universality, is not limited by raw materials and equipment, the available equipment has low cost, the preparation process is simple, the reaction condition is mild, the energy consumption is low, the production cost of aerogel is greatly reduced, and large-scale production is suitable.

[0146] There is no report in the prior art about using C m H n F x Cl y Br z solvent to prepare aerogel materials, and using the displacement-circulation effect of C m H n F x Cl y Br z solvent to solve the drying technology, cost and applicability problems that need to be solved in the practical application of aerogel materials, and in view of this, the present application is proposed.

Claims

1. A method for preparing an aerogel material, characterized in that, A gel material containing a first solvent and a second solvent are provided. The first solvent and the second solvent are replaced and separated through a solvent replacement-circulation process to obtain the aerogel material. The first solvent and the second solvent are miscible solvents; The solvent replacement-circulation process includes circulating the second solvent between gas and liquid states by controlling pressure or temperature to obtain the aerogel material; The first solvent comes into contact with the liquid second solvent and carries the first solvent away from the gel material; The second solvent changes from a liquid state to a gaseous state, causing the gel material to transform into the aerogel material; The solvent replacement-circulation process is a quasi-Carnot cycle, which includes four processes: compression, dissolution, expansion, and separation. In the solvent replacement-cycle process, the second solvent undergoes a two-state cycle, passing through both gaseous and liquid states. The second solvent is C m H n F x Cl y Br z The solvent, wherein the relationship between the number of atoms m, n, x, y, and z is 2m+2=n+x+y+z, where m≤2; The first solvent is the same as that of C. m H n F x Cl y Br z Polar and / or nonpolar solvents that are miscible with the solvent.

2. The method for preparing the aerogel material according to claim 1, characterized in that, The compression process in the solvent replacement-circulation process includes liquefying the second solvent by pressurizing or cooling; the dissolution process in the solvent replacement-circulation process includes the second solvent in liquid form contacting the gel material and dissolving the first solvent therein; the expansion process in the solvent replacement-circulation process includes changing the second solvent in liquid form from liquid to gaseous form by heating or depressurizing; and the separation process in the solvent replacement-circulation process is the separation of the second solvent from the first solvent.

3. The method for preparing the aerogel material according to claim 2, characterized in that, During the expansion process of the solvent replacement-cycle process, the heating or decompression is carried out by gradient decompression or by stepwise heating, so that the second solvent is transformed from a liquid state to a gaseous state to obtain the aerogel material.

4. The method for preparing the aerogel material according to claim 1, characterized in that, During the compression process, the C m H n F x Cl y Br z The solvent is liquefied under a pressure of 3~5MPa; or, liquefied at a temperature of -60℃.

5. The method for preparing the aerogel material according to claim 1, characterized in that, During the dissolution process, the C m H n F x Cl y Br z The solvent remains liquid under a pressure of 3~5MPa or a temperature of -20~60℃ and comes into contact with the gel material.

6. The method for preparing the aerogel material according to claim 1, characterized in that, During the expansion process, the pressure is reduced to atmospheric pressure via a gradient, or the temperature is increased to room temperature via a stepwise heating process, wherein C m H n F x Cl y Br z The solvent changes from a liquid state to a gaseous state.

7. The method for preparing the aerogel material according to claim 1, characterized in that, During the separation process, the C is subjected to room temperature or atmospheric pressure conditions. m H n F x Cl y Br z The solvent remains in a gaseous state.

8. The method for preparing the aerogel material according to claim 1, characterized in that, The gel material transforms into the aerogel material at room temperature and pressure.

9. The method for preparing the aerogel material according to any one of claims 1-8, characterized in that, It also includes a solvent replacement step; the solvent replacement step includes: replacing the gel material containing a solvent that is immiscible with the second solvent with the first solvent by a solvent replacement method to obtain the gel material containing the first solvent.

10. The method for preparing the aerogel material according to claim 9, characterized in that, The gel material includes one or more of the following: polyamide gel, polyurethane gel, polyester gel, cellulose gel, polyether gel, carbon material gel, and silica gel; the morphology of the gel material is a derivative morphology of any one or more of the following: powder, fiber, film, and bulk.

11. An aerogel material, prepared by the preparation method according to any one of claims 1-10, wherein the aerogel has a porous structure, including any one or more mixed gels selected from polyamide aerogel, polyurethane aerogel, polyester aerogel, cellulose aerogel, polyether aerogel, carbon material aerogel, and silica aerogel; and the morphology of the aerogel material is a derivative morphology of any one or more of the following: powder, fiber, film, and bulk.

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