Preparation method of low-carbon-emission silicon dioxide aerogel

Abstract

The application provides a preparation method of low-carbon-emission silica aerogel and belongs to the field of silica aerogel materials. The preparation method of low-carbon-emission silica aerogel comprises the following steps: (1) mixing fly ash and a carbonate and then calcining to obtain a calcination product; (2) immersing the calcination product obtained in step (1) in an acid-alcohol mixture, then standing and aging to obtain an aging gel; the immersion, standing and aging are carried out at room temperature; (3) sequentially subjecting the aging gel obtained in step (2) to alcoholization, hydrophobic modification, n-hexane replacement and drying to obtain low-carbon-emission silica aerogel; the alcoholization, hydrophobic modification and n-hexane replacement are carried out at room temperature. The preparation method of low-carbon-emission silica aerogel can significantly reduce the cost and carbon emission, and the prepared silica aerogel has a high specific surface area and a low thermal conductivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silica aerogel materials, in particular to a preparation method of low-carbon silica aerogel. BACKGROUND

[0002] Silica aerogel is a new type of porous material with controllable structure, which has many advantages, such as continuous network structure, nanoscale pores, high porosity and high specific surface area. These characteristics endow silica aerogel with unique properties, such as low density, low thermal conductivity, low refractive index, strong adsorption, etc., which makes it widely used in many fields. Fly ash is a waste produced in the production of coal industry, mainly composed of dust and particulate matter generated during the combustion of coal. Excessive fly ash emissions without proper utilization can cause serious environmental problems. However, fly ash is rich in silicon elements, which can be used as a silicon source for the preparation of aerogels, providing potential for resource comprehensive utilization.

[0003] The prior art "A method for preparing silica-alumina aerogel by dry preparation at normal pressure using fly ash as raw material" (Chinese patent, application number CN200910216385.4, publication date June 02, 2010) uses fly ash as a silicon source, which is calcined, sol-gel prepared, and then subjected to chlorine removal with flowing water during the gel process, followed by replacement, surface modification, and normal pressure drying to obtain silica aerogel. Surface modification is carried out at a temperature of 40-150℃, and normal pressure drying is carried out at a temperature of 40-150℃ for 2-10h. This prior art uses a higher temperature in surface modification to improve the performance (such as specific surface area) of the final prepared silica aerogel, but the higher temperature in the preparation process produces higher carbon emissions, and the performance of the prepared silica aerogel needs to be further improved. SUMMARY

[0004] The present application aims to provide a preparation method of low-carbon silica aerogel. The preparation method of low-carbon silica aerogel provided by the present application can reduce cost and carbon emissions, and the prepared low-carbon silica aerogel has a higher specific surface area and a lower thermal conductivity.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of low-carbon silica aerogel, comprising the following steps:

[0007] (1) mixing fly ash and carbonate and calcining to obtain a calcined product;

[0008] (2) the calcined product obtained in step (1) is impregnated with an acid-alcohol mixture, and then is left to stand and aged to obtain an aged gel; the impregnation, standing and aging are carried out at room temperature;

[0009] (3) the aged gel obtained in step (2) is subjected to alcoholization, hydrophobic modification, n-hexane replacement and drying in sequence to obtain the low-carbon-emission silica aerogel; the alcoholization, hydrophobic modification and n-hexane replacement are carried out at room temperature.

[0010] Preferably, in step (1), the carbonate is sodium carbonate or calcium carbonate; the mass ratio of the fly ash to the carbonate is 1:(0.5-1.5).

[0011] Preferably, in step (1), the calcination temperature is 800-1100℃, and the calcination time is 0.5-2h.

[0012] Preferably, in step (2), the acid-alcohol mixture is a mixture of hydrochloric acid / sulfuric acid, ethanol and water.

[0013] Preferably, in step (2), the concentration of hydrogen ions in the acid-alcohol mixture is 4-8mol / L.

[0014] Preferably, in step (2), the solid-liquid ratio of impregnation is 1Kg:(3-10)L, and the impregnation time is 10-90min.

[0015] Preferably, in step (3), the alcoholization, hydrophobic modification and n-hexane replacement are independently carried out for 12-72h.

[0016] Preferably, in step (3), the mass of the aged gel to the volume of the alcoholization liquid used for alcoholization is 1Kg:(0.5-2)L.

[0017] Preferably, in step (3), the mass of the aged gel to the volume of the hydrophobic modification liquid used for hydrophobic modification is 1Kg:(0.5-2)L.

[0018] Preferably, the hydrophobic modification liquid is a mixed solution of n-hexane, trimethylchlorosilane and anhydrous ethanol; the volume ratio of the n-hexane, trimethylchlorosilane and anhydrous ethanol is (4-16):2:1.

[0019] Preferably, in step (3), the mass of the aged gel to the volume of the n-hexane used for n-hexane replacement is 1Kg:(0.5-2)L.

[0020] The present application provides a preparation method of a low-carbon-emission silica aerogel, comprising the following steps:

[0021] (1) mixing fly ash and carbonate and calcining to obtain a calcined product; (2) immersing the calcined product obtained in step (1) in an acid-alcohol mixture, and then standing and aging to obtain an aged gel; the immersing, standing and aging are performed at room temperature; (3) sequentially subjecting the aged gel obtained in step (2) to alcoholization, hydrophobic modification, n-hexane replacement and drying to obtain a low-carbon-emission silica aerogel; the alcoholization, hydrophobic modification and n-hexane replacement are performed at room temperature. 2 / g, and a thermal conductivity of 0.021-0.023 W / m·k, which can significantly reduce the cost and carbon emission, and the prepared low-carbon-emission silica aerogel has a high specific surface area and a low thermal conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The figure is a process flow diagram for preparing the low-carbon-emission silica aerogel in the embodiments of the present application. DETAILED DESCRIPTION

[0023] The present application provides a preparation method of a low-carbon-emission silica aerogel, comprising the following steps:

[0024] (1) mixing fly ash and carbonate and calcining to obtain a calcined product;

[0025] (2) immersing the calcined product obtained in step (1) in an acid-alcohol mixture, and then standing and aging to obtain an aged gel; the immersing, standing and aging are performed at room temperature;

[0026] (3) sequentially subjecting the aged gel obtained in step (2) to alcoholization, hydrophobic modification, n-hexane replacement and drying to obtain a low-carbon-emission silica aerogel; the alcoholization, hydrophobic modification and n-hexane replacement are performed at room temperature.

[0027] The present application mixes fly ash and carbonate and calcines to obtain a calcined product.

[0028] In the present application, the carbonate is preferably sodium carbonate or calcium carbonate; the mass ratio of fly ash and carbonate is preferably 1:(0.5-1.5), more preferably 1:(0.8-1.2). The present application limits the type of carbonate and the mass ratio of fly ash and carbonate to the above range, which can ensure that the fly ash and carbonate produce a relatively complete reaction, which is conducive to the subsequent preparation of silica sol.

[0029] In the present application, the calcination temperature is preferably 800-1100℃, more preferably 900-1000℃; the calcination time is preferably 0.5-2h, more preferably 1-1.5h. The present application limits the calcination temperature and time to the above range, which can ensure the reaction to proceed, avoiding incomplete reaction caused by too low temperature or time, and avoiding high carbon emissions and energy waste caused by too high temperature or time.

[0030] In the present application, the chemical reaction during calcination is:

[0031] 3Na2CO3+3Al2O3·2SiO2→2NaAlSiO4+4NaAlO2+3CO2↑

[0032] NaAlO2+SiO2→NaAlSiO4

[0033] Al2O3+Na2CO3→2NaAlO2+CO2↑

[0034] Na2CO3+2SiO2+Al2O3→2NaAlSiO4+CO2↑

[0035] Na2CO3+SiO2→Na2SiO3+CO2↑

[0036] After obtaining the calcination product, the present application uses an acid-alcohol mixture to impregnate the calcination product, then stands and ages to obtain an aged gel.

[0037] In the present application, the impregnation, standing and aging are carried out at room temperature.

[0038] In the present application, the acid-alcohol mixture is preferably a mixture of hydrochloric acid / sulfuric acid, ethanol and water; the concentration of hydrogen ions in the acid-alcohol mixture is preferably 4-8mol / L. In the present application, water and ethanol in the acid-alcohol mixture act as solvents for hydrochloric acid, and the addition of ethanol can reduce the entry of metal ions in the calcination product into the solution, avoiding the reduction of the grid strength of the gel, while avoiding the reduction of the specific surface area and the increase of the thermal conductivity of the silica aerogel. The present application limits the composition of the acid-alcohol mixture and the concentration of the acid to the above range, which can ensure the subsequent reaction to proceed, while ensuring the silica aerogel to have a high specific surface area and a low thermal conductivity.

[0039] In the present application, the solid-liquid ratio of the impregnation is preferably 1 Kg:(3-10) L, more preferably 1 Kg:(5-8) L; the time of the impregnation is preferably 10-90 min, more preferably 30-60 min. In the present application, the use of the acid-alcohol mixture can reduce the content of metal ions in the solution after acid leaching. If the proportion of the acid-alcohol mixture is too small, the calcined product cannot be completely reacted; if the proportion is too large, the content of silica in the subsequent gel is too small, which reduces the grid strength of the gel and causes the specific surface area of the aerogel to decrease and the thermal conductivity to increase; if the impregnation time is too short, the reaction of the substance is incomplete; if the impregnation time is too long, the solution produces a gel phenomenon and is not easy to filter and separate the filtrate. The present application limits the solid-liquid ratio of the impregnation and the impregnation time to the above range, which can ensure that the aerogel with good performance is obtained.

[0040] In the present application, the chemical reaction in the impregnation process is:

[0041] NaAlSiO4+4HC1→NaCl+A1Cl3+H4SiO4

[0042] Na2SiO3+2HC1→2NaCl+H2SiO3

[0043] Na2CO3+2HC1→2NaCl+H2O+CO2↑

[0044] Preferably, after the end of the impregnation, the present application filters the impregnation mixture, and then sequentially places and ages the obtained impregnation filtrate.

[0045] In the present application, the time of the placement is preferably 2-10 days, more preferably 4-8 days. The present application can generate a gel through the placement.

[0046] In the present application, the aging is preferably carried out by standing in water; the time of the aging is preferably 1-4 days, more preferably 2-3 days. The present application can make the adjacent hydroxyl groups in the network polymerize on the surface of the network, form Si-O-Si groups from two Si-OH, produce a dehydration shrinkage phenomenon, and improve the gel strength. The present application adopts the method of standing in water to age the gel, avoids the use of flowing water for rinsing after the aging, simplifies the preparation process, and reduces the complex requirements for equipment and operation. The present application can remove the residual metal ions and chloride ions in the gel by washing the gel with water, and completely removes other impurities in the gel except silica.

[0047] After obtaining the aged gel, the present application sequentially carries out alcoholization, hydrophobic modification, n-hexane replacement, and drying on the aged gel, to obtain a low-carbon silica aerogel.

[0048] In the present application, the alcoholization, hydrophobic modification, and n-hexane replacement are carried out at room temperature.

[0049] The aging gel is aged for 12-72 hours, preferably 24-36 hours, and the ratio of the mass of the aging gel to the volume of the alcohol solution used for the aging is 1 Kg:(0.5-2) L, preferably 1 Kg:(1-1.5) L. In the present application, the alcohol solution used for the aging is preferably an aqueous solution of ethanol, methanol, n-butanol, n-propanol or isopropanol, and the volume concentration of the alcohol solution is preferably 40-100%. The present application limits the ratio of the mass of the aging gel to the volume of the alcohol solution, the aging time, and the type and concentration of the alcohol solution to the above ranges, so that the alcohol solution can replace water and enter the mesh pores of the silica in the gel, and the hydrogel is changed into an alcohol gel, which is beneficial to the modification of the subsequent gel.

[0050] In the present application, the hydrophobic modification is performed for 12-72 hours, preferably 24-36 hours, and the ratio of the mass of the aging gel to the volume of the hydrophobic modification solution used for the hydrophobic modification is 1 Kg:(0.5-2) L, preferably 1 Kg:(1-1.5) L. The hydrophobic modification solution is preferably a mixed solution of n-hexane, trimethylchlorosilane and anhydrous ethanol, and the volume ratio of the n-hexane, trimethylchlorosilane and anhydrous ethanol is (4-16):2:1, preferably (6-10):2:1. The present application can change the gel from hydrophilic to hydrophobic by the hydrophobic modification, which not only changes the properties of the gel, but also is beneficial to the subsequent drying step. The shrinkage of the gel after the hydrophobic modification during the drying stage is small, and the performance of the aerogel is improved.

[0051] In the present application, the n-hexane replacement is performed for 12-72 hours, preferably 24-36 hours, and the ratio of the mass of the aging gel to the volume of the n-hexane used for the n-hexane replacement is 1 Kg:(0.5-2) L, preferably 1 Kg:(1-1.5) L. The present application limits the n-hexane replacement time to the above range to ensure complete replacement. The present application uses the low liquid surface tension of n-hexane to replace the alcohol solution in the pores of the gel, which is beneficial to ensuring that the gel mesh structure does not collapse during drying, and the alcohol aging, hydrophobic modification and n-hexane replacement are all performed at room temperature, which improves the specific surface area of the gel, reduces the density and the thermal conductivity.

[0052] In the present application, the drying is preferably normal pressure drying, and the drying method is preferably directly standing or standing and then drying at room temperature to obtain low-carbon dioxide emission silica aerogel.

[0053] In the present application, when the drying method is direct standing, the standing time is preferably 2-11 days. The present application limits the drying method to direct standing to reduce the amount of carbon dioxide emissions.

[0054] In the present application, when the drying method is baking after standing, the standing time is preferably 12-48h; the baking is preferably performed in an oven; the baking temperature is preferably 40-120℃; and the baking time is preferably 10-90min. The present application can further improve the performance of the silica aerogel by limiting the drying method to baking after standing.

[0055] In the present application, the carbon emissions in the preparation method of the low-carbon silica aerogel exist in the heat consumed by baking and drying in an oven and the carbon dioxide generated by the decomposition of sodium carbonate.

[0056] In the present application, the carbon emissions generated by the heat consumed by baking are:

[0057] E e1 = EF e × AC e1

[0058] E e1 is the CO2 emissions (tCO2) caused by the purchased electricity during baking; EF e is the emission factor of China regional power grid during the statistical period (t / MWh); and AC e1 is the net purchased electricity during baking during the statistical period (MWh).

[0059] The carbon emissions generated by the heat consumed by drying in an oven are:

[0060] E e2 = EF e × AC e2

[0061] E e2 is the CO2 emissions (tCO2) caused by the purchased electricity during baking; EF e is the emission factor of China regional power grid during the statistical period (t / MWh); and AC e2 is the net purchased electricity during baking during the statistical period (MWh).

[0062] The carbon emissions generated by the decomposition of sodium carbonate are:

[0063] E m1 = M 碳酸钠 × 44 / 106.

[0064] In the present application, the total carbon emissions in the preparation method of the low-carbon silica aerogel are:

[0065] E = E e1 + E e2 + E m1 .

[0066] In the embodiment of the present application, the preparation process of the low-carbon silica aerogel is as shown in the following figure: Figure 1

[0067] The fly ash is mixed with sodium carbonate and calcined to obtain a calcined mixture. The calcined mixture is mixed with an acid-alcohol mixture to obtain a silica sol. The silica sol is aged at room temperature to obtain a hydrogel (aged gel). After ethanol replacement (alcoholization) and surface modification (hydrophobic modification and n-hexane replacement), the hydrogel is dried at normal pressure to obtain an aerogel (silica aerogel).

[0068] The present application uses fly ash as a silicon source, thereby reducing the preparation cost. The fly ash is calcined and then reacted with an acid-alcohol mixture, thereby increasing the specific surface area of the aerogel and reducing the thermal conductivity. By using n-hexane replacement, the low liquid surface tension of n-hexane is used to ensure that the gel grid structure does not collapse during drying, so that the specific surface area of the gel can be increased and the thermal conductivity can be reduced by operating at room temperature. By directly standing and aging after immersion, the preparation process is simplified, and the complexity of the equipment and operation is reduced.

[0069] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0070] Embodiment 1

[0071] A preparation method of a low-carbon silica aerogel, comprising the following steps:

[0072] (1) fly ash and sodium carbonate are mixed at a mass ratio of 1:1 and then calcined at 1000℃ for 2h to obtain a calcined product;

[0073] (2) the calcined product obtained in step (1) is immersed in an acid-alcohol mixture for 30min, and then the immersion mixture is filtered to obtain an immersion filtrate. The immersion filtrate is left to stand for 2 days and then aged in deionized water for 2 days to obtain an aged gel. The solid-liquid ratio of the immersion is 1Kg:6L. The acid-alcohol mixture is preferably a mixture of sulfuric acid, ethanol and water. The concentration of hydrogen ions in the acid-alcohol mixture is 6mol / L, and the volume ratio of ethanol to water is 4:1. The immersion, standing and aging are performed at room temperature.

[0074] ​(3) placing the aged gel obtained in step (2) into anhydrous ethanol solution, standing for 24 h for alcoholization, then placing into a hydrophobic modification liquid for standing for 24 h for hydrophobic modification, and then placing into n-hexane for standing for 24 h for n-hexane replacement, and standing for 7 d at room temperature to obtain the low-carbon-emission silica aerogel; the hydrophobic modification liquid is a mixed solution of n-hexane, trimethylchlorosilane and anhydrous ethanol; the volume ratio of the n-hexane, trimethylchlorosilane and anhydrous ethanol is 8:2:1; the mass of the aged gel to the volume of the alcoholization liquid used for alcoholization is 1Kg:1L; the mass of the aged gel to the volume of the hydrophobic modification liquid is 1Kg:1L; the mass of the aged gel to the volume of the n-hexane used for n-hexane replacement is 1Kg:2L; the alcoholization, hydrophobic modification and n-hexane replacement are carried out at room temperature.

[0075] The tap density of the low-carbon-emission silica aerogel prepared in Example 1 is 0.15 g / cm 3 , the specific surface area is 781.9 m 2 / g, and the thermal conductivity is 0.021 W / m·k.

[0076] The carbon emission amount of Example 1 is:

[0077] The carbon emission amount generated by the heat consumed in calcination is:

[0078] E e1 = EF e × AC e1

[0079] E e1 is the CO2 emission amount (tCO2) caused by the purchased electricity during calcination; EF e is the emission factor of the China regional power grid in the statistical period (t / MWh); AC e1 is the net purchased electricity amount (MWh) during calcination in the statistical period;

[0080] EF e take the average emission factor of the national power grid in 2022 as 0.581 tCO2 / MWh;

[0081] AC e1 take the power consumption of the muffle furnace under the test condition of continuous heating at 4 kW for 2 h;

[0082] then E e1 = 0.004648 tCO2;

[0083] The carbon emission amount generated by the decomposition of sodium carbonate is:

[0084] E m1 = M 碳酸钠 × 44 / 106;

[0085] The muffle can calcine 10 kg of the mixture each time, M 碳酸钠 is 5 kg;

[0086] E m1 = 0.002076 tCO2;

[0087] The carbon emissions generated by the heat consumed in drying using the oven are:

[0088] E e2 = 0;

[0089] E e1 = E m1 + E e2 = 0.006723 tCO2

[0090] The content of SiO2 in the calcined mixture of fly ash and sodium carbonate is 11.7%, and the content of SiO2 in the residue after acid leaching extraction is 14.3%. The mass of the mixture before acid leaching is 10 kg, and the mass of the mixture after acid leaching is 4 kg. The extraction amount of SiO2 is 0.598 kg;

[0091] Therefore, 0.006723 tCO2 is generated for each 0.598 kg of aerogel produced, and 11.246 tCO2 is generated for each 1 t of aerogel produced.

[0092] Example 2

[0093] A method for preparing low-carbon-silica-aerogel, comprising the following steps:

[0094] (1) mixing fly ash and sodium carbonate in a mass ratio of 1:0.8, and calcining at 800°C for 2h to obtain a calcined product;

[0095] (2) impregnating the calcined product obtained in step (1) with an acid-alcohol mixture for 60 min, filtering the impregnated mixture to obtain an impregnated filtrate, and then placing the impregnated filtrate in deionized water for aging for 1 day after standing for 6 days to obtain an aged gel; the solid-liquid ratio of the impregnation is 1 kg:4 L; the acid-alcohol mixture is preferably a mixture of hydrochloric acid, ethanol and water; the concentration of hydrogen ions in the acid-alcohol mixture is 6 mol / L, and the volume ratio of anhydrous ethanol to water is 1:1; the impregnation, standing and aging are carried out at room temperature;

[0096] (3) placing the aging gel obtained in the step (2) into anhydrous ethanol solution, standing for alcoholization for 72 h, then placing into a hydrophobic modification liquid for standing for hydrophobic modification for 24 h, then placing into n-hexane for standing for n-hexane replacement for 12 h, standing for 24 h at room temperature after that, drying in an oven at 120℃ for 20 min, to obtain a low-carbon-emission silica aerogel; the hydrophobic modification liquid is a mixed solution of n-hexane, trimethylchlorosilane and anhydrous ethanol; the volume ratio of the n-hexane, trimethylchlorosilane and anhydrous ethanol is 4:2:1; the ratio of the mass of the aging gel to the volume of the alcoholization liquid used for alcoholization is 1Kg:1L; the ratio of the mass of the aging gel to the volume of the hydrophobic modification liquid is 1Kg:2L; the ratio of the mass of the aging gel to the volume of the n-hexane used for n-hexane replacement is 1Kg:1L; the alcoholization, hydrophobic modification and n-hexane replacement are carried out at room temperature.

[0097] The tap density of the low-carbon-emission silica aerogel prepared in Example 2 is 0.12 g / cm 3 , the specific surface area is 875.5 m 2 / g, and the thermal conductivity is 0.022 W / m·k.

[0098] The carbon emission amount of Example 2 is:

[0099] The carbon emission amount generated by the heat consumed for calcination is the same as that of Example 1:

[0100] E e1 = 0.004648 tCO2;

[0101] The carbon emission amount generated by the decomposition of sodium carbonate is:

[0102] E m1 = M 碳酸钠 × 44 / 106;

[0103] The muffle furnace can calcine 10 kg of the mixture each time, M 碳酸钠 is 4.44 kg;

[0104] E m1 = 0.001850 tCO2;

[0105] The carbon emission amount generated by the heat consumed for drying using the oven is:

[0106] E e2 = EF e × AC e2

[0107] EF e takes the average emission factor of 0.581 tCO2 / MWh of the national power grid in 2022;

[0108] ACe2 The power consumption of the oven under the rated power for 20 min of continuous heating in the test case; the rated power of the oven is 0.6 kW;

[0109] E e2 = 0.0001162tCO2

[0110] Then E = E e1 + E m1 + E e2 = 0.006498tCO2;

[0111] Wherein the content of SiO2 in the calcined mixture of fly ash and sodium carbonate is 12.6%, the content of SiO2 in the residue after acid leaching is 16.8%, the mass of the mixture before acid leaching is 10 kg, the mass of the mixture after acid leaching is 4.2 kg, and the extraction amount of SiO2 is 0.554 kg;

[0112] Then 0.006614tCO2 is generated for every 0.554 kg of aerogel, and 11.930tCO2 is generated for every 1t of aerogel.

[0113] Example 3

[0114] A preparation method of low-carbon-emission silica aerogel, comprising the following steps:

[0115] (1) mixing fly ash and sodium carbonate at a mass ratio of 1:1.2 and calcining at 1000℃ for 2h to obtain a calcined product;

[0116] (2) impregnating the calcined product obtained in step (1) with an acid-alcohol mixture for 90 min, then filtering the impregnated mixture to obtain an impregnated filtrate, and then placing the impregnated filtrate in deionized water for aging for 3 days to obtain an aged gel; the solid-liquid ratio of the impregnation is 1 Kg:7 L; the acid-alcohol mixture is preferably a mixture of hydrochloric acid, ethanol and water; the acid-alcohol mixture has a concentration of 5 mol / L of hydrochloric acid, and a volume ratio of anhydrous ethanol to water of 3:1; the impregnation, standing and aging are carried out at room temperature;

[0117] (3) the aging gel obtained in step (2) is placed in anhydrous ethanol solution, alcoholized for 48 h, then placed in a hydrophobic modification liquid for 24 h for hydrophobic modification, then placed in n-hexane for 18 h for n-hexane replacement, and then placed at room temperature for 48 h, and then dried in an oven at 80℃ for 30 min to obtain a low-carbon silica aerogel; the hydrophobic modification liquid is a mixed solution of n-hexane, trimethylchlorosilane and anhydrous ethanol; the volume ratio of n-hexane, trimethylchlorosilane and anhydrous ethanol is 6:2:1; the mass of the aging gel to the volume of the alcoholizing liquid used for alcoholizing is 1Kg:2L; the mass of the aging gel to the volume of the hydrophobic modification liquid is 1Kg:1L; the mass of the aging gel to the volume of the n-hexane used for n-hexane replacement is 1Kg:0.5L; the alcoholizing, hydrophobic modification and n-hexane replacement are carried out at room temperature.

[0118] The tap density of the low-carbon silica aerogel prepared in Example 3 is 0.14 g / cm 3 , the specific surface area is 836.3 m 2 / g, and the thermal conductivity is 0.023 W / m·k.

[0119] The carbon emission amount of Example 3 is:

[0120] The carbon emission amount generated by the heat consumed for calcination is the same as that of Example 1:

[0121] E e1 = 0.004648 tCO2;

[0122] The carbon emission amount generated by the decomposition of sodium carbonate is:

[0123] E m1 = M 碳酸钠 × 44 / 106;

[0124] The muffle furnace can calcine 10 kg of the mixture at a time, M 碳酸钠 is 5.45 kg;

[0125] E m1 = 0.002264 tCO2;

[0126] The carbon emission amount generated by the heat consumed for drying using the oven is:

[0127] E e2 = EF e × AC e2

[0128] EF e takes the average emission factor of 0.581 tCO2 / MWh of the national power grid in 2022;

[0129] ACe2 The power consumption of the oven under rated power for 20 min of continuous heating in the test case; the rated power of the oven is 0.6 kW;

[0130] E e2 = 0.0001743tCO2

[0131] E = E e1 + E m1 + E e2 = 0.008086tCO2

[0132] The content of SiO2 in the calcined mixture of fly ash and sodium carbonate is 10.2%, and the content of SiO2 in the residue after acid leaching is 12.3%. The mass of the mixture before acid leaching is 10 kg, and the mass of the mixture after acid leaching is 3.7 kg. The extraction amount of SiO2 is 0.554 kg;

[0133] Therefore, 0.008086tCO2 is generated for every 0.565 kg of aerogel produced, and 14.311tCO2 is generated for every 1t of aerogel produced.

[0134] Comparative Example 1

[0135] Comparative Example 1 differs from Example 1 in that no n-hexane replacement is performed, and the rest is the same as Example 1.

[0136] The tap density of the silica aerogel prepared in Comparative Example 1 is 0.28 g / cm 3 , the specific surface area is 690.2 m 2 / g, and the thermal conductivity is 0.053 W / m·k.

[0137] The carbon emission of Comparative Example 1 is:

[0138] The carbon emission generated by the heat consumed in calcination is:

[0139] E e1 = EF e × AC e1

[0140] E e1 is the CO2 emission (tCO2) caused by purchased electricity during calcination; EF e is the regional power grid emission factor in China (t / MWh) during the statistical period; AC e1 is the net purchased electricity during calcination (MWh) during the statistical period;

[0141] EF e Take the average emission factor of the national power grid in 2022 as 0.581tCO2 / MWh;

[0142] ACe1 The power consumption of the muffle furnace in the test case is 4 kW for 2 h of continuous heating;

[0143] E = 0.004648tCO2 e1

[0144] The carbon emissions generated by the decomposition of sodium carbonate are:

[0145] E = 0.004648tCO2 m1 碳酸钠 M = 5 kg m1 e2 E = 0

[0146] The muffle furnace can calcine 10 kg of the mixture each time, and M sodium carbonate is 5 kg;

[0147] E = 0.002076tCO2

[0148] The carbon emissions generated by the heat consumed in the drying oven are:

[0149] E = 0

[0150] E = E + E + E = 0.006723tCO2 e1 m1 e2

[0151] In the calcined mixture of fly ash and sodium carbonate, the content of SiO2 is 11.7%, and after acid leaching extraction, the content of SiO2 in the residue is 14.3%. The mass of the mixture before acid leaching is 10 kg, and the mass of the mixture after acid leaching is 4 kg. The extraction amount of SiO2 is 0.598 kg;

[0152] Therefore, 0.006723tCO2 is generated for every 0.598 kg of aerogel produced, and 11.246tCO2 is generated for every 1t of aerogel produced.

[0153] Comparative Example 2

[0154] A method for preparing a silica aerogel, comprising the following steps:

[0155] (1) mixing fly ash and sodium carbonate in a mass ratio of 1:0.8 and calcining at 800°C for 2 h to obtain a calcined product;

[0156] (2) immersing the calcined product obtained in step (1) in hydrochloric acid for 60 min, filtering the immersion mixture to obtain an immersion filtrate, and then placing the immersion filtrate in deionized water for aging for 1 day after standing for 6 days to obtain an aged gel; the solid-liquid ratio of the immersion is 1 kg:4 L; the molar concentration of the hydrochloric acid is 6 mol / L; the immersion, standing and aging are carried out at room temperature; ​​​​​​

[0157] (3) the aging gel obtained in step (2) is placed in anhydrous ethanol solution, and alcoholization is carried out by standing for 72 h, then placed in a hydrophobic modification liquid and hydrophobic modification is carried out by standing for 24 h, then placed in n-hexane and n-hexane replacement is carried out by standing for 12 h, after standing for 24 h at room temperature, dried in an oven at 120℃ for 20 min to obtain a silica aerogel; the hydrophobic modification liquid is a mixed solution of n-hexane, trimethylchlorosilane and anhydrous ethanol; the volume ratio of n-hexane, trimethylchlorosilane and anhydrous ethanol is 4:2:1; the mass of the aging gel to the volume of the alcoholization liquid used for alcoholization is 1Kg:1L; the mass of the aging gel to the volume of the hydrophobic modification liquid is 1Kg:2L; the mass of the aging gel to the volume of the n-hexane used for n-hexane replacement is 1Kg:1L; the alcoholization, hydrophobic modification and n-hexane replacement are carried out at room temperature.

[0158] The tap density of the silica aerogel prepared in Comparative Example 2 is 0.61 g / cm 3 , the specific surface area is 630.4 m 2 / g, and the thermal conductivity is 0.093 W / m·k.

[0159] The carbon emission amount of Comparative Example 2 is:

[0160] The carbon emission amount generated by the heat consumed in calcination is:

[0161] E e1 = 0.004648 tCO2;

[0162] The carbon emission amount generated by the decomposition of sodium carbonate is:

[0163] E m1 = M 碳酸钠 × 44 / 106;

[0164] The muffle furnace can calcine 10 kg of the mixture each time, M 碳酸钠 is 4.44 kg;

[0165] E m1 = 0.00185 tCO2;

[0166] The carbon emission amount generated by the heat consumed in drying using the oven is:

[0167] E e2 = 0.0001162 tCO2;

[0168] E = E e1 + E m1 + E e2 = 0.006614 tCO2

[0169] The SiO2 content in the calcined mixture of fly ash and sodium carbonate was 12.6%, and the SiO2 content in the residue after acid leaching was 16.8%. The mass of the mixture before acid leaching was 10 kg, the mass of the mixture after acid leaching was 4.2 kg, and the SiO2 extraction amount was 0.554 kg.

[0170] Therefore, producing 0.554 kg of silica aerogel will generate 0.006614 t CO2, and producing 1 t of aerogel will generate 11.930 t CO2.

[0171] Comparative Example 3

[0172] The difference between Comparative Example 3 and Example 1 is that the impregnation temperature in step (2) is 60°C and the standing temperature is 50°C; the alcoholization temperature in step (3) is 50°C, the hydrophobic modification temperature is 60°C, the n-hexane replacement temperature is 60°C, and after n-hexane replacement, it is dried in an oven at 80°C for 24 hours to obtain silica aerogel.

[0173] The tap density of the silica aerogel prepared in Comparative Example 3 was 0.15 g / cm³. 3 Its specific surface area is 774.1 m². 2 / g, with a thermal conductivity of 0.021W / m·k.

[0174] The carbon emissions of Comparative Example 3 are:

[0175] The carbon emissions generated by the heat consumed in calcination are the same as in Example 1:

[0176] E e1 =0.004648tCO2;

[0177] The carbon emissions from the decomposition of sodium carbonate are:

[0178] E m1 =M 碳酸钠 ×44 / 106;

[0179] The muffle furnace can calcine 10 kg of mixture at a time. 碳酸钠 It weighs 5kg;

[0180] Then E m1 =0.002076tCO2;

[0181] The carbon emissions generated by the heat consumed in drying using an oven are:

[0182] E e2 =0.00837tCO2;

[0183] The carbon emissions generated by the electricity consumed during impregnation are:

[0184] Ee3 = 0.000702 tCO2;

[0185] The carbon emission generated by the standing power consumption is:

[0186] E e4 = 0.000837 tCO2;

[0187] The carbon emission generated by the alcoholization power consumption is:

[0188] E e5 = 0.00837 tCO2;

[0189] The carbon emission generated by the hydrophobic modification power consumption is:

[0190] E e6 = 0.00837 tCO2;

[0191] The carbon emission generated by the n-hexane replacement power consumption is:

[0192] E e7 = 0.00837 tCO2;

[0193] Then E = E e1 + E m1 + E e2 + E e3 + E e4 + E e5 + E e6 + E e7 = 0.0576 tCO2;

[0194] The content of SiO2 in the calcined mixture of fly ash and sodium carbonate is 11.7%, and the content of SiO2 in the residue after acid leaching is 14.3%. The mass of the mixture before acid leaching is 10 kg, and the mass of the mixture after acid leaching is 4 kg. The extraction amount of SiO2 is 0.598 kg;

[0195] Therefore, 0.0576 tCO2 is generated for every 0.598 kg of aerogel produced, and 96.331 tCO2 is generated for every 1 t of aerogel produced.

[0196] The properties and carbon emissions of the silica aerogels prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0197] Table 1 Properties and carbon emissions of silica aerogels prepared in Examples 1-3 and Comparative Examples 1-3

[0198]

[0199] As shown in Table 1, the low-carbon silica aerogel prepared by the present invention can significantly reduce the carbon emissions during its preparation process while ensuring excellent properties.

[0200] The preparation method provided by this invention produces 1 ton of silica aerogel with CO2 emissions of 11.246–14.311 tonnes, and the resulting low-carbon-emission silica aerogel has a specific surface area of ​​781.9–875.5 m². 2 With a thermal conductivity of 0.021–0.023 W / m·K, it can significantly reduce costs and carbon emissions, and the prepared low-carbon silica aerogel has a high specific surface area and a low thermal conductivity.

[0201] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-carbon silica aerogel, comprising the following steps: (1) mixing fly ash and a carbonate and calcining the mixture to obtain a calcined product; (2) immersing the calcined product obtained in step (1) in an acid-alcohol mixture, and then allowing the product to stand and age, to obtain an aged gel; the immersing, standing and aging are performed at room temperature; (3) sequentially subjecting the aged gel obtained in step (2) to alcoholization, hydrophobic modification, n-hexane replacement and drying, to obtain a low-carbon silica aerogel; the alcoholization, hydrophobic modification and n-hexane replacement are performed at room temperature; wherein the acid-alcohol mixture in step (2) is a mixture of hydrochloric acid / sulfuric acid, ethanol and water; the ratio of the mass of the aged gel to the volume of the alcoholization liquid used in the alcoholization in step (3) is 1 Kg:(0.5-2) L; the ratio of the mass of the aged gel to the volume of the hydrophobic modification liquid used in the hydrophobic modification in step (3) is 1 Kg:(0.5-2) L; the hydrophobic modification liquid is a mixed solution of n-hexane, trimethylchlorosilane and anhydrous ethanol; the volume ratio of the n-hexane, trimethylchlorosilane and anhydrous ethanol is (4-16):2:1; the ratio of the mass of the aged gel to the volume of the n-hexane used in the n-hexane replacement in step (3) is 1 Kg:(0.5-2) L; the carbonate in step (1) is sodium carbonate or calcium carbonate; the ratio of the mass of the fly ash to the mass of the carbonate is 1:(0.5-1.5); the concentration of hydrogen ions in the acid-alcohol mixture in step (2) is 4-8 mol / L; the solid-liquid ratio of the immersing in step (2) is 1 Kg:(3-10) L, and the immersing time is 10-90 min; the time for the alcoholization, hydrophobic modification and n-hexane replacement in step (3) is independently 12-72 h. ​ ​ ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein: ​ 3. The method of claim 1, wherein: ​ 4. The method of claim 3, wherein: ​ 5. The method of claim 1, wherein: ​

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