Method for preparing silica aerogel by supercritical drying with high-pressure liquid medium

Abstract

The invention relates to a method for preparing silica aerogel by supercritical drying with a high-pressure liquid medium, which comprises the following steps of: (1) adding silicon tetrachloride and water to perform reaction with stirring under the acidic condition that the pH is between 3 and 5, adjusting the pH to be between 8 and 10 by using ammonia water, adding the water and ethanol to perform hydrolysis and polycondensation reaction to form alcogel; (2) loading the alcogel into a high-pressure reaction kettle, filling the high-pressure liquid medium into the reaction kettle, and slowlyraising the temperature to reach supercritical pressure after the reaction kettle is filled with the high-pressure liquid medium; and (3) slowly releasing gas medium while slowly raising the temperature until the pressure in the kettle and external atmosphere are balanced, opening the reaction kettle, taking the sample out and drying the sample. The method has the advantages of readily available raw materials, simple process and low cost, solves the problem of easy shrinkage cracking of the SiO2 aerogel when dry, and can stably improve the reaction speed at the same time.

Description

technical field

[0001] The invention relates to a method for preparing silica airgel, in particular to a method for preparing silica airgel by supercritical drying with a high-pressure liquid medium. Background technique

[0002] Silica aerogel has the characteristics of low density, large specific surface area, and high porosity, and is a new type of lightweight nanoporous material with broad prospects. Making full use of the excellent properties of aerogels, realizing the low cost of raw materials and the simplicity, safety and low cost of the preparation process, so that it can be mass-produced is the current research hotspot.

[0003] In recent years, research on silica aerogels has mainly focused on BASF and BESY in Germany, Los Alamos National Laboratory, Lawrence Livermore National Laboratory and Sandia National Laboratory in the United States, and Montpellier Materials in France. Research center, Swedish LUND company and universities in the United States, Germany, J...

Examples

Embodiment 1

[0015] Add 50ml of silicon tetrachloride and 100ml of water into a 500ml three-necked flask with a stirrer, adjust the pH value to 3 with dilute hydrochloric acid, stir well, and react for 1 hour; then add ammonia water to adjust the pH value to 8, add 150ml of water and 50ml of ethanol, stirred to form a gel. The prepared gel was loaded into an autoclave, and then high-pressure liquid CO 2 Fill the reactor, then slowly raise the temperature to 31.0°C, increase the pressure to 7.3MPa, continue to raise the temperature, and slowly release CO 2 gas until the pressure inside the reactor is balanced with the external pressure, open the reactor, take out the gel, put it in an oven, and dry it for 2 hours to obtain SiO 2 airgel.

Embodiment 2

[0017] Add 50ml of silicon tetrachloride and 100ml of water into a 500ml three-necked flask with a stirrer, adjust the pH value to 4 with dilute hydrochloric acid, stir well, and react for 1 hour; then add ammonia water to adjust the pH value to 9, add 150ml of water and 50ml of ethanol, stirred to form a gel. Put the prepared gel into the autoclave, then fill the autoclave with high-pressure liquid methane, then slowly raise the temperature to -83.0°C, increase the pressure to 4.6MPa, continue to heat up, and slowly release methane gas until the reaction autoclave Balance the pressure with the external pressure, open the reactor, take out the gel, put it in an oven, and dry it for 2 hours to obtain SiO 2 airgel.

Embodiment 3

[0019] Add 50ml of silicon tetrachloride and 100ml of water into a 500ml three-necked flask with a stirrer, adjust the pH value to 5 with dilute hydrochloric acid, stir well, and react for 1 hour; then add ammonia water to adjust the pH value to 10, add 150ml of water and 50ml of ethanol, stirred to form a gel. Put the prepared gel into the autoclave, then fill the autoclave with high-pressure liquid ethylene, then slowly raise the temperature to 9.5°C, increase the pressure to 5.1MPa, continue to heat up, and slowly release ethylene gas until the pressure in the autoclave reaches Equilibrate with the external pressure, open the reactor, take out the gel, put it in an oven, and dry it for 2 hours to obtain SiO 2 airgel.

technical field

[0001] The invention relates to a method for preparing silica airgel, in particular to a method for preparing silica airgel by supercritical drying with a high-pressure liquid medium. Background technique

[0002] Silica aerogel has the characteristics of low density, large specific surface area, and high porosity, and is a new type of lightweight nanoporous material with broad prospects. Making full use of the excellent properties of aerogels, realizing the low cost of raw materials and the simplicity, safety and low cost of the preparation process, so that it can be mass-produced is the current research hotspot.

[0003] In recent years, research on silica aerogels has mainly focused on BASF and BESY in Germany, Los Alamos National Laboratory, Lawrence Livermore National Laboratory and Sandia National Laboratory in the United States, and Montpellier Materials in France. Research center, Swedish LUND company and universities in the United States, Germany, J...

Examples

Embodiment 1

[0015] Add 50ml of silicon tetrachloride and 100ml of water into a 500ml three-necked flask with a stirrer, adjust the pH value to 3 with dilute hydrochloric acid, stir well, and react for 1 hour; then add ammonia water to adjust the pH value to 8, add 150ml of water and 50ml of ethanol, stirred to form a gel. The prepared gel was loaded into an autoclave, and then high-pressure liquid CO 2 Fill the reactor, then slowly raise the temperature to 31.0°C, increase the pressure to 7.3MPa, continue to raise the temperature, and slowly release CO 2 gas until the pressure inside the reactor is balanced with the external pressure, open the reactor, take out the gel, put it in an oven, and dry it for 2 hours to obtain SiO 2 airgel.

Embodiment 2

[0017] Add 50ml of silicon tetrachloride and 100ml of water into a 500ml three-necked flask with a stirrer, adjust the pH value to 4 with dilute hydrochloric acid, stir well, and react for 1 hour; then add ammonia water to adjust the pH value to 9, add 150ml of water and 50ml of ethanol, stirred to form a gel. Put the prepared gel into the autoclave, then fill the autoclave with high-pressure liquid methane, then slowly raise the temperature to -83.0°C, increase the pressure to 4.6MPa, continue to heat up, and slowly release methane gas until the reaction autoclave Balance the pressure with the external pressure, open the reactor, take out the gel, put it in an oven, and dry it for 2 hours to obtain SiO 2 airgel.

Embodiment 3

[0019] Add 50ml of silicon tetrachloride and 100ml of water into a 500ml three-necked flask with a stirrer, adjust the pH value to 5 with dilute hydrochloric acid, stir well, and react for 1 hour; then add ammonia water to adjust the pH value to 10, add 150ml of water and 50ml of ethanol, stirred to form a gel. Put the prepared gel into the autoclave, then fill the autoclave with high-pressure liquid ethylene, then slowly raise the temperature to 9.5°C, increase the pressure to 5.1MPa, continue to heat up, and slowly release ethylene gas until the pressure in the autoclave reaches Equilibrate with the external pressure, open the reactor, take out the gel, put it in an oven, and dry it for 2 hours to obtain SiO 2 airgel.