Silica aerogel with increased alkaline stability

Patent metadata

Field	Value
Publication number	US-12515958-B2
Application number	US-202117922203-A
Country	US
Kind code	B2
Filing date	Apr 20, 2021
Priority date	Apr 30, 2020
Publication date	Jan 6, 2026
Grant date	Jan 6, 2026

Abstract

The present invention relates to a process for producing a hydrophobized silica aerogel, comprising the following steps: a) preparing a hydrophobized silica gel comprising alkoxy groups; b) drying of the hydrophobized silica gel obtained in step a); c) treatment of the product obtained in step b) with a gas mixture comprising water and a base or an acid. A hydrophobized silica aerogel with a reduced alkoxy group content, suitable for thermal insulation applications, is also provided.

First claim

The invention claimed is:

1 . A process for producing a hydrophobized silica aerogel, comprising the following steps:
a) preparing a hydrophobized silica gel comprising alkoxy groups; b) drying the hydrophobized silica gel obtained in step a); c) treating the hydrophobized silica gel dried in step b) with a gas mixture comprising water and a base or an acid.

2 . The process of claim 1 , wherein the alkoxy groups are alkylalkoxy groups selected from the group consisting of: methoxy (OCH 3 ); ethoxy (OC 2 H 5 ); propoxy (OC 3 H 7 ); butoxy (OC 4 H 9 ); and mixtures thereof.

3 . The process of claim 1 , wherein the silica gel is obtained by hydrolysis of an organosilicate selected from the group consisting of: tetraethyl orthosilicate (TEOS); tetramethyl orthosilicate (TMOS); tetraisopropyl orthosilicate (TPOS); and mixtures or oligomers thereof.

4 . The process of claim 1 , wherein the silica gel is obtained by gelification of an inorganic precursor selected from the group consisting of: sodium silicate; waterglass; ion exchanged waterglass; silicic acid; colloidal silica; and mixtures thereof.

5 . The process of claim 1 , wherein step a) is carried out using a hydrophobizing agent activatable by an acid catalyst selected from the group consisting of: hydrogen chloride; nitric acid; sulfuric acid; trimethylchlorosilane; and mixtures thereof.

6 . The process of claim 5 , wherein step a) is carried out using a hydrophobizing agent selected from the group consisting of: hexamethyldisiloxane; trimethylethoxysilane; trimethylmethoxysilane; and mixtures thereof.

7 . The process of claim 1 , further comprising a gelation of the silica sol and optionally aging of the resulting silica gel in the presence of a base catalyst selected from the group consisting of: ammonia; ammonium fluoride; aminosilanes; and mixtures thereof.

8 . The process of claim 1 , wherein step b) is carried out under subcritical conditions.

9 . The process of claim 1 , wherein the base used in step c) of the process is selected from the group consisting of: ammonia; lower aliphatic alkylamines; and mixtures thereof.

10 . The process of claim 1 , wherein the acid used in step c) of the process is selected from the group consisting of: a volatile mineral acid; a carboxylic acid; a halosilane; and mixtures thereof.

11 . The process of claim 10 , wherein the volatile mineral acid is selected from the group consisting of: hydrochloric acid (HCl); hydrofluoric acid (HF); hydrobromic acid (HBr); hydroiodic acid (HI); and nitric acid (HNO 3 ); the carboxylic acid is formic acid or acetic acid; and the halosilane is trimethylchlorosilane.

12 . The process of claim 1 , wherein step c) is conducted at the temperature of 50° C.-250° C.

13 . The process of claim 1 , wherein the duration of step c) is 1 minute-1000 minutes.

14 . The process of claim 2 , wherein the silica gel is obtained by hydrolysis of an organosilicate selected from the group consisting of: tetraethyl orthosilicate (TEOS); tetramethyl orthosilicate (TMOS); tetraisopropyl orthosilicate (TPOS); and mixtures or oligomers thereof.

15 . The process of claim 2 , wherein the silica gel is obtained by gelification of an inorganic precursor selected from the group consisting of: sodium silicate; waterglass; ion exchanged waterglass; silicic acid; colloidal silica; and mixtures thereof.

16 . The process of claim 2 , wherein step a) is carried out using a hydrophobizing agent activatable by an acid catalyst selected from the group consisting of: hydrogen chloride; nitric acid; sulfuric acid; trimethylchlorosilane; and mixtures thereof.

17 . The process of claim 16 , wherein step a) is carried out using a hydrophobizing agent selected from the group consisting of: hexamethyldisiloxane; trimethylethoxysilane; trimethylmethoxysilane; and mixtures thereof.

Assignees

• Evonik Operations Gmbh

Inventors

• Numrich Uwe
• Bade Stefan
• Marion Nicolas
• Koebel Matthias
• Malfait Wim
• Hauser Stefanie
• Vogel Nicolas

Classifications

• C01B33/159

  Coating or hydrophobisation · CPC title

• C01B33/152

  Preparation of hydrogels · CPC title

• C01B33/1585 Primary

  Dehydration into aerogels · CPC title