A method for preparing environmentally friendly aerogel particles that can be used in aerogel mortar

Abstract

The application discloses a preparation method of environment-friendly aerogel particles for aerogel mortar, which comprises the following steps: placing wet gel particles and a drying medium in a drying kettle; the wet gel is composed of a gel skeleton and an intraparticle solvent, the intraparticle solvent is single or mixed alcohol, and the pore size is micro-nano level; the drying medium is single or mixed alcohol; and the purpose of removing the residual impurities in the aerogel particles is achieved by replacing the residual alcohol and by-product gas in the aerogel pores with an inert gas with a free path greater than the nanometer pore size of the aerogel. The prepared silica aerogel particles have remarkable advantages in environmental protection, and the low thermal conductivity, light weight, heat insulation, hydrophobicity and other characteristics make the silica aerogel particles have wide application prospect and environmental protection benefits in the field of environment-friendly mortar in the building field.

Description

Technical Field

[0001] This invention relates to the field of aerogel production, specifically to an environmentally friendly aerogel particle that can be used in aerogel mortar, its preparation method, and its application. Background Technology

[0002] Silica (SiO2) aerogel, due to its high porosity, low thermal conductivity, and low density, offers significant advantages in thermal insulation, sound insulation, noise reduction, and heat insulation. In the construction industry, energy conservation and low carbon emissions have become essential prerequisites for the development of the building industry. Compared with traditional insulation materials, aerogel materials have advantages such as extremely low thermal conductivity, flame retardancy or non-flammability, and lightweight. Aerogels or their derivatives can be flexibly applied to exterior walls, roofs, and windows, effectively reducing building energy consumption. Silica aerogel particles are one of the aerogel product series and can be used directly as fillers in aerogel glass, thermal insulation fillers in wall gaps, and as an important raw material for aerogel insulation mortar. Although silica aerogel has excellent performance, its preparation methods still have certain shortcomings, especially the industrial-scale preparation of SiO2 aerogel, which significantly limits its further promotion and application.

[0003] In the production and preparation technology of silica aerogel particles, compared with atmospheric pressure drying and supercritical carbon dioxide drying, high-temperature supercritical alcohol drying process has advantages such as simple process and high efficiency. However, since supercritical alcohol drying relies on the pressure difference between the inside and outside of the drying vessel to continuously release pressure, the pressure release rate will inevitably decrease in the low-pressure stage. At the same time, when the pressure release ends, residual alcohols or their high-temperature by-products remain in the pores of silica aerogel, which will result in high organic residue in the product and even an irritating odor, affecting its further application. Summary of the Invention

[0004] This invention aims to at least partially address one of the technical problems in related technologies. To this end, embodiments of this invention propose an environmentally friendly aerogel particle that can be used in aerogel mortar, a method for its preparation, and its application.

[0005] The present invention adopts the following technical solution:

[0006] Firstly,

[0007] This invention provides a method for preparing silica aerogel particles, comprising:

[0008] (1) Place the wet gel particles and the drying medium in a drying kettle; the wet gel consists of a gel skeleton and a solvent inside the pores, the solvent inside the pores is a single or mixed alcohol, and the pore size is micro-nano scale; the drying medium is a single or mixed alcohol.

[0009] (2) Apply heat to raise the temperature above the critical point temperature of the drying medium, and keep it at the temperature and pressure for 0.5 to 5 hours;

[0010] (3) Keep the temperature constant and depressurize at a rate of 1 to 5 MPa / h until the pressure enters a low-pressure area of ​​less than 1 MPa.

[0011] (4) Introduce an inert gas with a free path ≥50nm at room temperature and pressure to raise the pressure of the drying vessel to a medium pressure range of 1-5MPa, and maintain the temperature and pressure for 5-60 minutes.

[0012] (5) Release the pressure to a low-pressure area of ​​less than 1 MPa at a rate of 0.01 to 0.5 MPa / min;

[0013] (6) Repeat steps (4) and (5) multiple times to complete the impurity removal process;

[0014] (7) Reduce the temperature inside the drying kettle to 20-100°C, release the pressure to atmospheric pressure (usually 1 atm), remove the material, and obtain silica aerogel particles.

[0015] This invention relates to a high-temperature supercritical drying process for alcohols in the preparation of silica aerogel particles. It removes residual impurities from the aerogel particles by replacing the residual alcohols and their byproducts within the pores with an inert gas whose path of freedom is greater than the aerogel nanopore size. Because the aerogel particles obtained using this method contain an inert gas with a path of freedom greater than the aerogel nanopore size, the gas cannot flow freely within the nanopores, preventing gas loss. Simultaneously, the inert gas replaces the residual alcohols and their byproducts, improving the environmental friendliness of the silica aerogel particle product and reducing its calorific value, thus enhancing its thermal safety. Furthermore, the use of an inert gas ensures process safety at high temperatures compared to other types of gases.

[0016] Furthermore, during the experimental process, this invention discovered that adding an inert gas with a free path ≥50 nm to the low-pressure region (less than 1 MPa) of the drying vessel can more gently regulate the pressure, reducing structural collapse caused by internal stress changes in the aerogel due to rapid pressure changes (added in the medium-pressure region, where the external pressure is higher). This maintains the high porosity and structural integrity of the aerogel. Adding the gas in the low-pressure region (less than 1 MPa) helps improve the pore distribution and pore size of the aerogel, thereby enhancing its overall performance.

[0017] In some embodiments, the drying medium is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, glycerol, or tert-amyl alcohol. Preferably, the drying medium is one or more selected from methanol, ethanol, n-propanol, and n-butanol; more preferably, the drying medium is one or two selected from methanol and ethanol; and even more preferably, the drying medium is ethanol.

[0018] In some embodiments, the solvent within the pores is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, glycerol, or tert-amyl alcohol. Preferably, the solvent within the pores is one or more selected from methanol, ethanol, n-propanol, and n-butanol; more preferably, the solvent within the pores is one or two selected from methanol and ethanol; and even more preferably, the solvent within the pores is ethanol.

[0019] In some embodiments, the drying medium and the solvent inside the pore are the same.

[0020] In some embodiments, the total volume of the wet gel particles and the drying medium is 20% to 90% of the volume of the drying vessel. More preferably, it is 30% to 50%.

[0021] In some embodiments, the mass ratio of the wet gel particles to the drying medium is 1:(1-10), more preferably 1:(2-6), and even more preferably 1:(3-5).

[0022] In some embodiments, in step (2), heat is applied to raise the temperature to at least 1 to 5°C above the critical point temperature of the drying medium.

[0023] In some embodiments, the inert gas is one or more of N2, He, Ar, and air, or a combination of one or more of N2, He, Ar, and air with CO2. It is understood that the combined gas satisfies a path of freedom ≥ 50 nm. More preferably, the path of freedom of the inert gas is ≥ 60 nm, which is larger than the nanopore size of most aerogels, allowing it to be better contained within the nanopores of the aerogel and preventing leakage.

[0024] More preferably, the inert gas is one or more combinations of He, Ar, and N2. Using an inert gas will not chemically react with the materials in the aerogel. During the high-temperature drying process, it can effectively prevent the organic groups in the aerogel from undergoing pyrolysis or oxidation, thereby maintaining the original structure and properties of the aerogel material. Moreover, inert gases have higher safety at high temperatures.

[0025] More preferably, the inert gas is helium. Helium has strong diffusion ability in the supercritical state, which can more effectively penetrate into the pores of the wet gel, replacing the solvent and thus facilitating a more uniform pore structure. Furthermore, since the interaction between helium and the solvent is relatively weak, adding helium during the low-pressure stage of the supercritical drying process more thoroughly removes the solvent from the aerogel, reducing solvent residue and improving the purity and performance of the aerogel.

[0026] Preferably, in step (4), an inert gas is introduced to bring the pressure of the drying vessel to a medium pressure range of 1.5 to 5 MPa, more preferably 2 to 5 MPa, and even more preferably 2 to 3 MPa.

[0027] In some embodiments, the number of repetitions in step (6) is 2 to 5 times. More preferably, the number of repetitions is 3 or 4 times.

[0028] In some embodiments, in step (1), the wet gel is obtained by fully mixing a silicon source, a hydrophobic reagent, a solvent, and deionized water to obtain a mixture, adding an acidic catalyst and an alkaline catalyst to the mixture under stirring, fully gelling, granulating and sieving after gelation, adding a solvent to the sieved gel particles, and soaking the gel particles for aging.

[0029] The silicon source is one or more of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and isopropyl orthosilicate.

[0030] The hydrophobicating agent is one or more of methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, vinyltrichlorosilane, trimethylethoxysilane, hexamethyldisilazane, and hexamethyldisiloxane.

[0031] The solvent is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, glycerol, or tert-amyl alcohol. Preferably, the solvent is one or more selected from methanol, ethanol, n-propanol, and n-butanol; more preferably, the solvent is one or two selected from methanol and ethanol; even more preferably, the solvent is ethanol.

[0032] The acidic catalyst is one or more of hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, ammonium chloride, sodium bisulfate, ammonium sulfate, or ammonium fluoride.

[0033] The alkaline catalyst is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and ammonia water.

[0034] In some preferred embodiments, the silicon source is tetraethyl orthosilicate, the hydrophobicating agent is methyltriethoxysilane, the solvent is ethanol, the acidic catalyst is ammonium fluoride, and the alkaline catalyst is ammonia. In this embodiment, tetraethyl orthosilicate is used as the silicon source. The aerogel structure generated by the hydrolysis and condensation reaction is complete, with a uniform and reasonable pore size distribution, which is beneficial for building a stable microscopic channel structure and is a more suitable silicon source material for the system of this invention. Methyltriethoxysilane can improve the hydrophobicity of the aerogel and also affect the formation of the pore structure. Ethanol, as a solvent, helps dissolve and mix the silicon source and the hydrophobicating agent, promoting the uniformity of the reaction. The volatility of the solvent also affects the drying process of the gel, thereby further affecting the pore structure. Using ammonium fluoride and ammonia as composite catalysts is more conducive to the full cross-linking of the aerogel in the system of this invention and the construction of a stable pore structure, promoting the stability of the aerogel particle state, and improving the reaction rate and product uniformity.

[0035] Further, the mass ratio of the silicon source, hydrophobic reagent, solvent, and water is 1:(0.5-2):(5-7):(0.5-1.5); the mass ratio of the acidic catalyst to the mixture is 1:(100-230); and the mass ratio of the alkaline catalyst to the mixture is 1:(100-230).

[0036] In some embodiments, the aging temperature is 25–70°C, the time is 12–48 hours, and the amount of solvent added during the aging process is 40%–80% of the total mass of the gel particles.

[0037] Secondly,

[0038] This invention also provides silica aerogel particles, which are prepared by the above-described preparation method.

[0039] In some embodiments, the silica gel particles have an adjustable particle size range of 0.1–15 mm, an average pore size ≤20 nm, a porosity ≥90%, a specific surface area ≥600 m² / g, and a density of 35–50 kg / m³. 3 The thermal conductivity at 25℃ is 13–18 mW / m·K; the weight loss rate at 105℃ is ≤0.5%.

[0040] More preferably, the porosity is ≥94%; the density is 35–40 kg / m³. 3 The thermal conductivity at 25℃ is 14~16mW / m·K.

[0041] Thirdly,

[0042] The embodiments of the present invention also provide the use of the above-mentioned aerogel particles in the preparation of thermal insulation materials;

[0043] In some embodiments of the application, the silica gel particles are used to prepare aerogel mortar.

[0044] In some embodiments of the application, the silica gel particles constitute 65-95% of the mixture excluding water, where the percentage is by volume. More preferably, it is 65-80%.

[0045] The advantages and beneficial effects of this invention are as follows:

[0046] (1) In the high-temperature supercritical drying process of silica aerogel particles, this invention removes residual impurities from the aerogel particles by replacing the residual alcohols and their byproduct gases within the aerogel pores with an inert gas whose free path is greater than the aerogel nanopore size. Because the aerogel particles obtained by this method contain an inert gas with a free path greater than the aerogel nanopore size, the gas within the aerogel nanopores cannot flow freely and is not easily lost. Simultaneously, the inert gas replaces the residual alcohols and their byproduct gases within the aerogel pores, improving the environmental friendliness of the silica aerogel particle product and reducing the calorific value of the aerogel particles, thus improving the product's thermal safety. Furthermore, under high-temperature conditions, the use of an inert gas ensures process safety compared to other types of gases.

[0047] (2) By selecting the silicon source, hydrophobic reagent, solvent, acid catalyst and alkaline catalyst of silica aerogel particles in the preferred reaction system, and by optimizing the high temperature alcohol supercritical drying process, the silica aerogel particles prepared by this invention have significant advantages in terms of environmental protection. Moreover, their low thermal conductivity, lightweight, heat insulation and hydrophobicity make them have broad application prospects and environmental benefits in environmentally friendly mortar in the construction field. Attached Figure Description

[0048] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0049] Figure 1 This is a photograph of the silica aerogel prepared in Example 1.

[0050] Figure 2 This is a SEM image of the silica aerogel prepared in Example 1.

[0051] Figure 3 This is a graph showing the relationship between the free path and pressure of various gases at 20℃.

[0052] Figure 4 This is a physical image of the aerogel mortar prepared in Application Example 1. Detailed Implementation

[0053] The embodiments of the present invention are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0054] In this document, the terms "first aspect," "second aspect," and "third aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0055] In this article, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0056] In this document, terms such as "preferred," "more preferred," and "better" are used only to describe implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0057] In this document, terms such as "further" and "even further" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0058] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0059] In this document, the term "wet gel" refers to a gel in which the movable interstitial phase within a network of interconnected pores is primarily formed by a liquid phase (such as a conventional solvent). In embodiments of the invention, the conventional solvent refers to an alcohol solvent. Aerogels typically require the initial preparation of a wet gel, followed by drying to obtain the aerogel.

[0060] In this document, the disclosure of numerical ranges includes all values ​​across the entire range and the disclosure of further subdivisions of the ranges, including the endpoints and subranges given for these ranges.

[0061] Unless otherwise specified, all raw materials and equipment mentioned in this article are those that can be manufactured commercially or by known methods; and all methods mentioned are conventional methods unless otherwise specified.

[0062] In the production and preparation technology of silica aerogel particles, the high-temperature supercritical drying process of alcohols has advantages such as simple process and high efficiency. Commonly used drying media include methanol, ethanol, n-propanol, and n-butanol. Table 1 shows the critical pressure and critical temperature information of four commonly used alcohols.

[0063] Table 1 Critical pressure and critical temperature of four commonly used alcohols

[0064] Critical pressure 8.09 Mpa 6.14 Mpa 5.17 Mpa 4.43 Mpa Critical temperature 239.52℃ 240.75℃ 263.6℃ 289.85℃

[0065] Taking ethanol as an example, the free path of ethanol gas at room temperature and pressure is about 20 nm, which is close to the nanopore size of some aerogels (reported in the literature as 10-50 nm). This results in residual ethanol gas having a certain degree of fluidity in aerogel nanopores with a pore size >20 nm. At this time, organic residual gases such as ethanol are continuously released from the aerogel particles into the surrounding environment, which affects the use of the product to a certain extent.

[0066] Figure 3 The graphs showing the relationship between the free path and pressure for various gases (at 20°C) are presented. Table 2 lists the free path of different gases at 20°C and 1 atm.

[0067] Table 2. Free path of different gases at 20℃ and 1 atm

[0068] Free path / nm 60.20 177.65 63.16 38.98 65.83 20.73

[0069] In this invention, high-free-range inert gases such as N2, He, and Ar, or mixtures of inert gases and inert gases (such as CO2) are used (the characteristic of the above single or mixed gases is: free-range > 50 nm). By repeatedly filling and replacing the gas under high temperature conditions, the residual ethanol in the nanopores of the aerogel particles is rapidly replaced, thereby removing volatile impurities from the aerogel particles, reducing odor, and lowering the calorific value of the aerogel particles.

[0070] Example 1

[0071] A method for preparing silica aerogel particles includes the following steps:

[0072] Mix 100g tetraethyl orthosilicate, 150g methyltriethoxysilane, 600g ethanol, and 150g deionized water. Stir for 30 minutes, then add 10g ammonium fluoride and 10g ammonia water. Stir for another 30 minutes to allow for complete gelation. Place the gel on a 5-mesh vibrating screen for crushing at a vibration frequency of 1400 rpm and a vibration amplitude of 0-3mm. The crushed gel particles should be less than or equal to 4mm. Add 70% ethanol (by weight of the total gel mass) to the granulated gel particles and soak them for one day of aging. Then, perform supercritical drying to form aerogel particles.

[0073] The specific process of supercritical drying is as follows:

[0074] S1: Place 500g of wet gel particles and 2000g of ethanol in a drying vessel; the total volume of the wet gel particles and ethanol is 40% of the volume of the drying vessel.

[0075] S2: Heat to 245℃ (the pressure will also change accordingly, reaching 6.5 MPa at this point), and maintain the temperature and pressure for 3 hours;

[0076] S3: Maintain a constant temperature and depressurize at a rate of 2 MPa / h until the pressure reaches 0.8 MPa (entering a low-pressure region of less than 1 MPa);

[0077] S4: Introduce He gas to raise the pressure of the drying kettle to 2 MPa (medium pressure zone), and maintain the temperature and pressure for 30 minutes;

[0078] S5: Release pressure to 0.8 MPa at a rate of 0.03 MPa / min (entering a low-pressure region of less than 1 MPa);

[0079] S6: Repeat steps S4 and S5 3 times to complete the impurity removal process;

[0080] S7: Reduce the temperature inside the drying kettle to 40°C, release the pressure to atmospheric pressure (usually 1 atm), remove the material, and obtain silica aerogel particle product.

[0081] Figure 1 This is a photograph of the silica aerogel prepared in Example 1. Figure 2 This is a SEM image of the silica aerogel prepared in Example 1. (The image is obtained through...) Figure 1 and Figure 2 As can be seen, the aerogel particles exhibit a pale blue transparent appearance due to Rayleigh scattering, and the appearance is uniform. SEM images show the microstructure of the aerogel, characterizing its surface morphology at the nanoscale. The network structure is clearly visible, and the pore structure is uniform, with all pores falling within the micropore range.

[0082] Example 2

[0083] The difference from Example 1 is that the inert gas introduced in step S4 is N2. The gas free path is 60.2 nm.

[0084] Example 3

[0085] The difference from Example 1 is that the inert gas introduced in step S4 is Ar. The gas free path is 63.16 nm.

[0086] Example 4

[0087] The difference from Example 1 is that in step S6, the step is repeated twice.

[0088] Example 5

[0089] The difference from Example 1 is that the silicon source is methyl orthosilicate. The hydrophobicating agent is trimethylethoxysilane. The solvent is methanol. The acidic catalyst is hydrochloric acid. The basic catalyst is sodium bicarbonate.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that in step S2, the heat preservation and pressure holding time is 0.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that in Comparative Example 2, an inert gas was added at the pressure release point to the medium pressure region of 2.5 MPa. The specific process of Comparative Example 2 is as follows:

[0094] S1: Place 500g of wet gel particles and 2000g of ethanol in a drying vessel; the total volume of the wet gel particles and ethanol is 40% of the volume of the drying vessel.

[0095] S2: Heat to 245℃ (the pressure will also change accordingly, reaching 6.5 MPa at this point), and maintain the temperature and pressure for 3 hours;

[0096] S3: Maintain a constant temperature and depressurize at a rate of 2 MPa / h until the pressure reaches 2.5 MPa;

[0097] S4: Introduce He gas to raise the pressure of the drying kettle to 4 MPa, and maintain the temperature and pressure for 30 minutes;

[0098] S5: Depressurize at a rate of 2 MPa / h until the pressure reaches 2.5 MPa;

[0099] S6: Repeat steps S4 and S5 3 times;

[0100] S7: Depressurize at a rate of 2 MPa / h until the pressure reaches 0.8 MPa;

[0101] S8: Reduce the temperature inside the drying vessel to 40°C, release the pressure to atmospheric pressure (usually 1 atm) at a rate of 0.03 MPa / min, remove the material, and obtain silica aerogel particle product.

[0102] The products of the embodiments and comparative examples were tested, and the results are shown in Table 3.

[0103] Table 3

[0104]

[0105] As can be seen from the data in Examples 1-3, by using high-free-path inert gases He, N2, and Ar to repeatedly fill and replace the residual ethanol in the nanopores of aerogel particles under high-temperature conditions, the prepared aerogel products all have the characteristics of low thermal conductivity, low density, and high porosity. In comparison, He has a stronger diffusion ability and can more effectively penetrate into the pores of the wet gel to replace the solvent, which is conducive to obtaining a more uniform and stable pore structure, higher porosity, and lower product density.

[0106] The data from Examples 1 and 4 show that Example 1 was repeated 3 times, while Example 4 was repeated 2 times. Compared to Example 4, the inert gas He in Example 1 more fully replaced the drying medium, leaving less residue, which is more conducive to obtaining a more uniform pore structure and improving the purity and performance of the aerogel. This is reflected in the performance, meaning Example 1 has a lower thermal conductivity and lower density.

[0107] As can be seen from the data of Examples 1 and 5, in the preparation system of Example 5, the silicon source is methyl orthosilicate and the hydrophobic reagent is trimethylethoxysilane. In Example 5, because more methyl groups were introduced, a more compact network structure was formed, the average pore size was reduced, and the product density was increased.

[0108] The data from Example 1 and Comparative Example 1 show that the product performance of Comparative Example 1 is poor (increased thermal conductivity, increased density, and decreased porosity). The reason for this is that the heat transfer inside the drying vessel is uneven, and the central part may not be able to reach the supercritical state or may drift near the critical point, resulting in poor drying effect and uneven density distribution inside, which in turn affects the overall product performance.

[0109] The data from Example 1 and Comparative Example 2 show that the product performance of Comparative Example 2 is poor (high thermal conductivity, high density, and low porosity). The reason for this is that the addition of an inert gas in the medium-pressure zone is insufficient to fully displace the drying medium inside the particles, resulting in residues that affect the overall product performance.

[0110] Application Example 1

[0111] A method for preparing aerogel mortar includes the following steps:

[0112] S1: Weigh the silica aerogel particles prepared in Example 1, polyethylene fiber, organosilane hydrophobic agent, citric acid and dispersant, white cement, and quicklime in a volume fraction of 85:1.1:1.3:3.8:6.1:1.2;

[0113] S2: After weighing the raw materials, dry them at 75℃ for 30 minutes and then add them to the mixer and mix for 20 minutes.

[0114] S3: Mix the mixture with water at a mass ratio of 2:1.5, continue stirring for 10 minutes, and then pour into the mold. (See Figure 4 for the actual product.)

[0115] S4: Curing samples according to the national standard GB / T20473-2021 for building thermal insulation mortar—air temperature (21-25)℃, relative humidity (45-55)%, and then testing the compressive strength, thermal conductivity, and other properties of the samples.

[0116] Application Comparative Example 1

[0117] The difference from Application Example 1 is that Application Comparative Example 1 uses the silica aerogel particle product of Comparative Example 1 to prepare thermal insulation mortar.

[0118] Application Comparative Example 2

[0119] The difference from Application Example 1 is that Application Comparative Example 2 uses the silica aerogel particle product of Comparative Example 2 to prepare thermal insulation mortar.

[0120] Application Comparative Example 3

[0121] The difference from Application Example 1 is that Application Comparative Example 3 uses silica aerogel particles prepared by conventional supercritical drying of ethanol to prepare thermal insulation mortar.

[0122] The method for preparing silica aerogel particles includes the following steps:

[0123] Mix 100g tetraethyl orthosilicate, 150g methyltriethoxysilane, 600g ethanol, and 150g deionized water. Stir for 30 minutes, then add 10g ammonium fluoride and 10g ammonia water. Stir for another 30 minutes to allow for complete gelation. Place the gel on a 5-mesh vibrating screen for crushing. Vibration frequency: 1400 r / min; vibration amplitude: 0-3 mm. The crushed gel particles should be less than or equal to 4 mm. Add 70% ethanol (by weight of the total gel mass) to the granulated gel particles and soak for 1 day of aging. Then, perform conventional supercritical ethanol drying at a heating rate of 65℃ / h to reach 255℃, while simultaneously increasing the pressure to 8 MPa. Hold at this temperature for 2 hours, then depressurize and cool to obtain the final product.

[0124] Table 4 Performance of Thermal Insulation Mortar

[0125]

[0126] By comparing the data from Application Example 1 and Application Comparative Examples 1-3, it can be seen that the thermal insulation mortar prepared in Application Example 1 has good thermal insulation performance, good mechanical strength and bonding strength, low water absorption, and good water resistance.

[0127] The application of Comparative Example 1 (due to insufficient drying during the preparation of silica aerogel particles), Comparative Example 2 (due to insufficient replacement of inactive gases during drying, resulting in residual drying medium inside), and Comparative Example 3 (conventional supercritical drying with residual drying medium inside) ultimately resulted in poor overall mortar performance.

[0128] In Application Example 1, volatile gases were detected according to the national standard GB50325-2020, and analysis was performed using gas chromatography-mass spectrometry (GC-MS). The results are shown in Table 5.

[0129] Table 5

[0130] Formaldehyde mg / m 3 ]] 0.021 mg / m 3 ]] 0.012 Toluene mg / m 3 ]] 0.011 Xylenes mg / m 3 ]] 0.010 Ammonia mg / m3 0.031 Radon Bq / m 3 ]] 0.006 TVOC mg / m 3 ]] 0.035

[0131] The results showed that the detected value of volatile gases in the thermal insulation mortar product prepared using Example 1 met the standard requirements and was far below the limit. Furthermore, the TVOC content of Comparative Example 3 (0.125 mg / m³) was significantly lower. 3 The comparison shows that the drying method of the present invention effectively solves the problems of residual alcohols or their high-temperature by-products in the pores of silica aerogel, high organic residue in the product, and even irritating odor.

[0132] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0133] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing silica aerogel particles, characterized in that, include: (1) The wet gel particles and the drying medium are placed in a drying kettle; the wet gel consists of a gel skeleton and a solvent in the pores, the solvent in the pores is a single or mixed alcohol, and the pore size is micro-nano scale; the drying medium is a single or mixed alcohol. (2) Apply heat to raise the temperature above the critical point temperature of the drying medium, and keep it at the temperature and pressure for 0.5~5 hours; (3) Keep the temperature constant and depressurize at a rate of 1~5 MPa / h until the pressure enters a low-pressure area of ​​less than 1 MPa; (4) Inert gas with a free path ≥50nm at room temperature and pressure is introduced to raise the pressure of the drying vessel to the medium pressure range of 1~5Mpa, and the temperature and pressure are maintained for 5~60min; (5) Release the pressure at a rate of 0.01~0.5 MPa / min to a low-pressure area of ​​less than 1 MPa; (6) Repeat steps (4) and (5) multiple times to complete the impurity removal process; (7) Reduce the temperature inside the drying kettle to 20~100℃, release the pressure to atmospheric pressure, take out the material, and obtain silica aerogel particles.

2. The method for preparing silica aerogel particles according to claim 1, characterized in that, The drying medium is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, glycerol, or tert-amyl alcohol. And / or, the solvent inside the pore is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, glycerol, or tert-amyl alcohol.

3. The method for preparing silica aerogel particles according to claim 2, characterized in that, The drying medium is one or more of methanol, ethanol, n-propanol, and n-butanol; And / or, the solvent inside the pore is one or more of methanol, ethanol, n-propanol, and n-butanol.

4. The method for preparing silica aerogel particles according to claim 3, characterized in that, The drying medium is one or both of methanol and ethanol; And / or, the solvent inside the pore is one or both of methanol and ethanol.

5. The method for preparing silica aerogel particles according to claim 4, characterized in that, The drying medium is ethanol; And / or, the solvent inside the pore is ethanol.

6. The method for preparing silica aerogel particles according to claim 2, characterized in that, The drying medium and the solvent inside the pore are selected in the same way.

7. The method for preparing silica aerogel particles according to claim 1, characterized in that, The total volume of the wet gel particles and the drying medium is 20% to 90% of the volume of the drying vessel; the mass ratio of the wet gel particles to the drying medium is 1:(1 to 10).

8. The method for preparing silica aerogel particles according to claim 7, characterized in that, The total volume of the wet gel particles and the drying medium is 30% to 50% of the volume of the drying vessel.

9. The method for preparing silica aerogel particles according to claim 7, characterized in that, The mass ratio of the wet gel particles to the drying medium is 1:(2~6).

10. The method for preparing silica aerogel particles according to claim 9, characterized in that, The mass ratio of the wet gel particles to the drying medium is 1:(3~5).

11. The method for preparing silica aerogel particles according to claim 1, characterized in that, The inert gas is one or more of N2, He, Ar, and air, or a combination of one or more of N2, He, Ar, and air with CO2.

12. The method for preparing silica aerogel particles according to claim 11, characterized in that, The free path of the inert gas is ≥60 nm.

13. The method for preparing silica aerogel particles according to claim 11, characterized in that, The inert gas is one or more combinations of He, Ar, and N2.

14. The method for preparing silica aerogel particles according to claim 13, characterized in that, The inert gas mentioned is helium.

15. The method for preparing silica aerogel particles according to claim 1, characterized in that, In step (2), heat is applied to make the temperature exceed the critical point temperature of the drying medium by 1°C; And / or, in step (4), an inert gas is introduced to bring the pressure of the drying vessel to a medium pressure range of 1.5~5 MPa; And / or, the number of repetitions in step (6) is 2 to 5 times.

16. The method for preparing silica aerogel particles according to claim 15, characterized in that, In step (4), an inert gas is introduced to bring the pressure in the drying vessel to a medium pressure range of 2-5 MPa; And / or, the number of repetitions in step (6) is 3 or 4.

17. The method for preparing silica aerogel particles according to claim 16, characterized in that, In step (4), an inert gas is introduced to bring the pressure of the drying vessel to a medium pressure range of 2-3 MPa.

18. A method for preparing silica aerogel particles according to claim 1, characterized in that, In step (1), the wet gel is obtained by fully mixing silicon source, hydrophobic reagent, solvent and deionized water to obtain a mixture, adding acid catalyst and alkaline catalyst to the mixture under stirring, fully gelling, granulating and sieving after gelation, adding solvent to the sieved gel particles and soaking the gel particles for aging. The silicon source is one or more of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and isopropyl orthosilicate. The hydrophobicating agent is one or more of methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, vinyltrichlorosilane, trimethylethoxysilane, hexamethyldisilazane, and hexamethyldisiloxane; The solvent is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, glycerol, or tert-amyl alcohol. The acidic catalyst is one or more of hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, ammonium chloride, sodium bisulfate, ammonium sulfate, or ammonium fluoride. The alkaline catalyst is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and ammonia water.

19. A method for preparing silica aerogel particles according to claim 18, characterized in that, The silicon source is tetraethyl orthosilicate, the hydrophobic reagent is methyltriethoxysilane, the solvent is ethanol, the acidic catalyst is ammonium fluoride, and the alkaline catalyst is ammonia.

20. A method for preparing silica aerogel particles according to claim 18 or 19, characterized in that, The mass ratio of the silicon source, hydrophobic reagent, solvent, and water is 1:(0.5~2):(5~7):(0.5~1.5); the mass ratio of the acidic catalyst to the mixture is 1:(100~230); and the mass ratio of the alkaline catalyst to the mixture is 1:(100~230).

21. The method for preparing silica aerogel particles according to claim 20, characterized in that, The aging temperature is 25~70℃, the time is 12~48 hours, and the amount of solvent added during the aging process is 40%~80% of the total mass of the gel particles.

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