Method for preparing aluminum oxide-silicon oxide composite aerogel through normal-pressure drying

Abstract

The invention provides a method for preparing aluminum oxide-silicon oxide composite aerogel through normal-pressure drying. The method comprises the following steps: respectively preparing silica sol and aluminum sol by taking tetraethoxysilane as a silicon source and aluminum chloride hexahydrate as an aluminum source, mixing the silica sol and the aluminum sol, heating and stirring to obtain mixed sol, adding epoxypropane into the mixed sol, and standing until the sol does not flow to obtain composite gel; soaking the composite gel in ethanol and normal hexane in sequence for aging and solvent exchange; and uniformly mixing a modifier, a catalyst and a solvent to prepare a modification solution, soaking the composite gel in the modification solution for modification, and then washing and drying through normal hexane to obtain the aluminum oxide-silicon oxide composite aerogel. According to the preparation method, inorganic aluminum chloride hexahydrate is used as an aluminum source, trimethylethoxysilane is used as a modifier, and the aluminum oxide-silicon oxide composite aerogel is prepared through normal-pressure drying. The prepared aluminum oxide-silicon oxide composite aerogel still has a mesoporous structure and a high specific surface area after being subjected to high-temperature heat treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of composite aerogel preparation, and relates to a method for preparing aluminum oxide-silicon oxide composite aerogel by drying at normal pressure. Background Art

[0002] Alumina aerogel is a nanoporous material with the characteristics of low density and low thermal conductivity. It can still have a high porosity and a large specific surface area at high temperatures. Therefore, it has broad application prospects in industrial kilns, aerospace and other fields. However, due to the phase change of alumina, the specific surface area of ​​alumina aerogel drops sharply after heat treatment at a temperature exceeding 1000°C. Therefore, maintaining the nanoporous structure and specific surface area of ​​aerogel at high temperatures is the key work of alumina aerogel. Adding silicon oxide to alumina to prepare composite aerogel can inhibit the growth of alumina particles during heat treatment, thereby maintaining the performance of aerogel at high temperatures. The present invention adopts an innovative method, using inorganic aluminum chloride hexahydrate as an aluminum source, trimethylethoxysilane as a modifier, and hydrochloric acid as a catalyst to achieve atmospheric pressure drying preparation of alumina-silicon oxide composite aerogel. The alumina-silicon oxide composite aerogel prepared by the method of the present invention has excellent performance. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing alumina-silica composite aerogel by drying at normal pressure. The aluminum source used in the method is inorganic aluminum chloride hexahydrate, and the alumina-silica composite aerogel is prepared by a normal pressure drying method.

[0004] The present invention is carried out according to the following steps:

[0005] (1) According to the molar ratio of 1: (4-20): (3-5): (2*10 -3 ~6*10 -3 ) TEOS, ethanol, water and HCl are mixed, and stirred continuously for 30 to 180 minutes at 50° C. to obtain silica sol; aluminum chloride hexahydrate, ethanol and water are mixed in a molar ratio of 1: (4 to 20): (8 to 24), and stirred continuously for 30 to 90 minutes at 50° C. to obtain aluminum sol; TEOS is mixed with aluminum sol in a molar percentage of (TEOS + aluminum chloride hexahydrate) = (30% to 60%), and stirred continuously for 30 to 90 minutes at 50° C. 180min, to obtain a mixed sol; adding propylene oxide to the mixed sol according to the molar ratio of propylene oxide: aluminum chloride hexahydrate = 8:1, and standing until the composite gel no longer flows, to obtain a silicon oxide-aluminum oxide composite gel; soaking the composite gel in ethanol and n-hexane successively for aging and solvent exchange, the single soaking time of each solvent is 8 to 16h, each solvent is soaked 2 to 4 times, the soaking temperature is 40°C, and the volume of each soaking solvent is 0.5 to 2.0 times the volume of the composite gel;

[0006] (2) mixing a solvent, a modifier, and a catalyst to prepare a modification solution, placing the composite gel after aging and solvent exchange in step (1) into the modification solution for modification, the modification temperature being 60° C. and the modification time being 12 to 36 hours;

[0007] (3) soaking and washing the modified composite gel in step (2) in n-hexane for 8 to 16 hours, 2 to 4 times, at a temperature of 40° C., with the volume of n-hexane being 0.5 to 2.0 times the volume of the modified composite gel;

[0008] (4) placing the composite gel after soaking and washing in step (3) into a drying oven for normal pressure drying at 60° C. and 100° C. for 24 h, respectively, to obtain an alumina-silicon oxide composite aerogel.

[0009] In step (2), the solvent is n-hexane, the modifier is trimethylethoxysilane, the catalyst is 37% hydrochloric acid by mass, the total volume of the modified solution is 0.8 to 1.5 times the volume of the composite gel after aging and solvent exchange in step (1), the amount of trimethylethoxysilane added is 0.8 to 2.5 times the molar number of (ethyl orthosilicate + aluminum chloride hexahydrate), and the amount of catalyst hydrochloric acid added is 1 / 300 to 1 / 60 of the volume of the composite gel.

[0010] Compared with the prior art, the technical advantages of the present invention are as follows:

[0011] The aluminum source is inorganic aluminum chloride hexahydrate, which is low-cost and easy to control; the atmospheric pressure drying preparation process is simple to operate and suitable for expanded production; the modifier used is chlorine-free modifier trimethylethoxysilane, which does not release corrosive gas HCl and can reduce the corrosion of equipment during the drying process. The aluminum oxide-silicon oxide composite aerogel prepared by this method has a high specific surface area and can still maintain a porous structure after heat treatment at 800℃ and 1000℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the N2 adsorption-desorption isotherm diagram of the alumina-silica composite aerogel sample after heat treatment at different temperatures.

[0013] Figure 2 This is a comparison curve of specific surface area, average pore size and pore volume of alumina-silicon oxide composite aerogel samples after heat treatment at different temperatures. DETAILED DESCRIPTION

[0014] The present invention is further described in detail below with reference to specific embodiments, and some characterization results are presented.

[0015] Example 1

[0016] 0.04 mol of tetraethyl orthosilicate, 0.64 mol of ethanol, 0.16 mol of water and 0.01 mL of hydrochloric acid (37%) were mixed, and the mixture was stirred continuously for 120 min at 50°C to obtain silica sol; 0.08 mol of aluminum chloride hexahydrate, 1.28 mol of ethanol and 1.6 mol of water were mixed, and the mixture was stirred continuously for 60 min at 50°C to obtain aluminum sol; the silica sol and the aluminum sol were mixed, and the mixture was stirred continuously for 90 min at 50°C to obtain a mixed sol; 0.64 mol of propylene oxide was added to the mixed sol, and the mixture was allowed to stand until the composite gel no longer flowed, to obtain a silicon oxide-aluminum oxide composite gel; the composite gel was successively immersed in 180 mL of ethanol and n-hexane for aging and solvent exchange, and each The single immersion time in the solvent is 12 hours, and the gel is immersed in ethanol for 4 times and in n-hexane for 2 times, and the immersion temperature is 40°C; 0.18 mol of trimethylethoxysilane and 0.5 mL of hydrochloric acid (37%) are added to n-hexane to prepare a modification solution with a total volume of 200 mL, and the composite gel after aging and solvent exchange is placed in the modification solution and immersed at 60°C for modification for 24 hours; the modified composite gel is immersed and washed in 180 mL of n-hexane for 12 hours, and is immersed and washed twice in total, and the immersion and washing temperature is 40°C; the composite gel after immersion and washing is placed in a drying oven for normal pressure drying, and is dried at 60°C and 100°C for 24 hours, respectively, to obtain an alumina-silica composite aerogel.

[0017] In the method for preparing alumina-silicon oxide composite aerogel by drying at normal pressure provided in this embodiment, the thermal conductivity of the alumina-silicon oxide composite aerogel obtained at 25°C is 0.0542 W / (m*K) and the specific surface area is 714.86 m 2 / g, average pore diameter of 5.81nm, pore volume of 1.04cm 3 / g; after the aerogel was heat treated at 800℃ for 2h, the specific surface area was 539.21m 2 / g, the average pore diameter is 6.91nm, and the pore volume is 0.93cm 3 / g; after the aerogel was heat treated at 1000℃ for 2h, the specific surface area was 127.15m 2 / g, average pore diameter is 10.22nm, pore volume is 0.33cm 3 / g.

[0018] The above effect parameters of the following two embodiments are basically the same as those of embodiment 1, and are very close, so only the thermal conductivity is listed.

[0019] Example 2

[0020] 0.04 mol of tetraethyl orthosilicate, 0.64 mol of ethanol, 0.16 mol of water and 0.01 mL of hydrochloric acid (37%) were mixed, and the mixture was stirred continuously for 120 min at 50°C to obtain silica sol; 0.08 mol of aluminum chloride hexahydrate, 1.28 mol of ethanol and 1.6 mol of water were mixed, and the mixture was stirred continuously for 60 min at 50°C to obtain aluminum sol; the silica sol and the aluminum sol were mixed, and the mixture was stirred continuously for 90 min at 50°C to obtain a mixed sol; 0.64 mol of propylene oxide was added to the mixed sol, and the mixture was allowed to stand until the composite gel no longer flowed, to obtain a silicon oxide-aluminum oxide composite gel; the composite gel was successively immersed in 180 mL of ethanol and n-hexane for aging and solvent exchange, and each The single immersion time in the solvent is 12 hours, and the gel is immersed in ethanol for 4 times and in n-hexane for 2 times, and the immersion temperature is 40°C; 0.24 mol trimethylethoxysilane and 0.5 mL hydrochloric acid (37%) are added to n-hexane to prepare a modification solution with a total volume of 200 mL, and the composite gel after aging and solvent exchange is placed in the modification solution and immersed at 60°C for modification for 24 hours; the modified composite gel is immersed and washed in 180 mL n-hexane for 12 hours, and is immersed and washed twice in total, and the immersion and washing temperature is 40°C; the composite gel after immersion and washing is placed in a drying oven for normal pressure drying, and is dried at 60°C and 100°C for 24 hours, respectively, to obtain an alumina-silica composite aerogel.

[0021] In the method for preparing alumina-silica composite aerogel by drying at normal pressure provided in this embodiment, the thermal conductivity of the obtained alumina-silica composite aerogel at 25° C. is 0.0514 W / (m*K).

[0022] Example 3

[0023] 0.04 mol of tetraethyl orthosilicate, 0.64 mol of ethanol, 0.16 mol of water and 0.01 mL of hydrochloric acid (37%) were mixed, and the mixture was stirred continuously for 120 min at 50°C to obtain silica sol; 0.04 mol of aluminum chloride hexahydrate, 0.64 mol of ethanol and 0.64 mol of water were mixed, and the mixture was stirred continuously for 60 min at 50°C to obtain aluminum sol; the silica sol and the aluminum sol were mixed, and the mixture was stirred continuously for 90 min at 50°C to obtain a mixed sol; 0.32 mol of propylene oxide was added to the mixed sol, and the mixture was allowed to stand until the composite gel no longer flowed, to obtain a silicon oxide-aluminum oxide composite gel; the composite gel was successively immersed in 180 mL of ethanol and n-hexane for aging and solvent exchange, and each The single immersion time in the solvent is 12 hours, and the gel is immersed in ethanol for 4 times and in n-hexane for 2 times, and the immersion temperature is 40°C; 0.16 mol trimethylethoxysilane and 0.75 mL hydrochloric acid (37%) are added to n-hexane to prepare a modification solution with a total volume of 200 mL, and the composite gel after aging and solvent exchange is placed in the modification solution and immersed at 60°C for modification for 24 hours; the modified composite gel is immersed and washed in 180 mL n-hexane for 12 hours, and is immersed and washed twice in total, and the immersion and washing temperature is 40°C; the composite gel after immersion and washing is placed in a drying oven for normal pressure drying, and is dried at 60°C and 100°C for 24 hours, respectively, to obtain an alumina-silica composite aerogel.

[0024] In the method for preparing alumina-silicon oxide composite aerogel by drying at normal pressure provided in this embodiment, the thermal conductivity of the obtained alumina-silicon oxide composite aerogel at 25° C. is 0.0609 W / (m*K).

[0025] Figure 1 The N2 adsorption-desorption isotherms of the alumina-silicon oxide composite aerogel sample prepared in Example 1 after heat treatment at different temperatures; Figure 2 The pore size distribution curves of the alumina-silica composite aerogel samples prepared in Example 1 after heat treatment at different temperatures. It can be seen that the N2 adsorption-desorption isotherms of the alumina-silica composite aerogel samples after heat treatment at different temperatures all belong to Type IV isotherms. At higher relative pressures, capillary condensation occurs between N2 and the aerogel surface, resulting in a sharp increase in the amount of N2 adsorbed. A hysteresis loop appears in the isotherm, indicating that the alumina-silica composite aerogel sample prepared in Example 1 has a typical mesoporous structure. After heat treatment at 800°C and 1000°C, respectively, the N2 adsorption of the alumina-silica composite aerogel decreased, especially after heat treatment at 1000°C, the maximum adsorption of the sample increased from 671cm before heat treatment to 25.87cm. 3 / g down to 210cm 3 / g, but the sample still has a mesoporous structure. The alumina-silicon oxide composite aerogel without high temperature heat treatment has a mesoporous structure of 714.86m 2 / g and a specific surface area of ​​1.04cm 3 / g pore volume, the pore structure is well developed. After heat treatment at 800℃, the pore volume of alumina-silicon oxide composite aerogel does not change significantly, and the specific surface area is reduced to 539.21m 2 After heat treatment at 1000℃, the specific surface area and pore volume of alumina-silicon oxide composite aerogel still retain 127.15m 2 / g and 0.33cm 3 / g.

Claims

1. A method for preparing alumina-silicon oxide composite aerogel by drying at normal pressure, characterized in that: The following steps are included: (1) According to the molar ratio of 1: (4-20): (3-5): (2*10 -3 ~6*10 -3 ) TEOS, ethanol, water and HCl are mixed and stirred at 50°C for 30 to 180 minutes to obtain silica sol; aluminum chloride hexahydrate, ethanol and water are mixed in a molar ratio of 1: (4 to 20): (8 to 24) and stirred at 50°C for 30 to 90 minutes to obtain aluminum sol; silica sol and aluminum sol are mixed in a molar percentage of TEOS: (TEOS + aluminum chloride hexahydrate) = (30% to 60%) and stirred at 50°C for 30 minutes. ~180min, to obtain a mixed sol; adding propylene oxide to the mixed sol according to the molar ratio of propylene oxide: aluminum chloride hexahydrate = 8:1, and standing until the composite gel no longer flows to obtain a silicon oxide-aluminum oxide composite gel; soaking the composite gel in ethanol and n-hexane for aging and solvent exchange, the single soaking time of each solvent is 8 to 16h, each solvent is soaked 2 to 4 times, the soaking temperature is 40°C, and the volume of each soaking solvent is 0.5 to 2.0 times the volume of the composite gel; (2) mixing a solvent, a modifier, and a catalyst to prepare a modification solution, placing the composite gel after aging and solvent exchange in step (1) into the modification solution for modification, the modification temperature being 60° C., and the modification time being 12 to 36 hours; the solvent being n-hexane, the modifier being trimethylethoxysilane, and the catalyst being 37% hydrochloric acid by mass, the total volume of the prepared modification solution being 0.8 to 1.5 times the volume of the composite gel after aging and solvent exchange in step (1), the amount of trimethylethoxysilane added being 0.8 to 2.5 times the molar number of (ethyl orthosilicate + aluminum chloride hexahydrate), and the amount of catalyst hydrochloric acid added being 1 / 300 to 1 / 60 of the volume of the composite gel; (3) soaking and washing the modified composite gel in step (2) in n-hexane for 8 to 16 hours, 2 to 4 times, at a temperature of 40° C., with the volume of n-hexane being 0.5 to 2.0 times the volume of the modified composite gel; (4) placing the composite gel after soaking and washing in step (3) into a drying oven for normal pressure drying at 60° C. and 100° C. for 24 h respectively to obtain an alumina-silicon oxide composite aerogel.

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