Method for producing silicon dioxide silica aerogel by drying in atmosphere pressure with rice hull as raw material

Abstract

The invention discloses a drying preparation method of silicon dioxide aerogel under atmospheric pressure, using rice husk as raw material, which comprises the following procedures: (1) preparation of rice husk sol; (2) aging of gel; (3) solvent exchange; (4) surface modification of gel; (5) drying under atmospheric pressure. Instead of expensive toxicant organ silicon source, agricultural trashes rice husk is used as raw material, thus greatly reduce the cost; instead of super-critical drying, drying under atmospheric pressure greatly reduces the requirements for the whole process on the equipment, greatly improves the safety performance on one hand, also greatly reduces the running cost on the other. The method in the invention has the advantages of simple technology, easy operation, which is suitable for scale production.

Description

technical field [0001] The invention relates to the field of preparation of chemical materials, in particular to a preparation method of silica airgel. Background technique [0002] Rice husk is a large amount of agricultural waste. my country produces about 200 million tons of rice every year, of which the quality of rice husk accounts for about 20%. Because the rice husk fibrous tissue is covered with hard silicic acid, its nutritional value is extremely low, and its digestible nutrients are all negative, and it is easy to cause gastrointestinal diseases in animals. Due to the high lignin and silicon content, the rice husk is not easy to absorb water, and it is not easy to rot when it is directly applied to the field as fertilizer. This characteristic limits its development and utilization. Now, only a very small amount of rice husk has been utilized. For example, Wenzhou Wusulijiang Rice Industry Co., Ltd. built a power plant with an annual generating capacity of 5 mill...

AI Technical Summary

Problems solved by technology

while SiO 2 The surface hydrophobization treatment process of airgel is also the process in which -OH is replaced by hydrophobic groups, and the organosilicon compound orthosilicate [Si(OR) 4 ] or alkyl silicates [R 4-n Si(OR) n ], will make Si(OH) 4 Hydrophobic groups replace the hydroxyl-OH sol in the gel before cross-linking and polymerization, so it is difficult to form a complete gel network structure, resulting in high apparent density and small specific surface area of ​​the airgel prepared by this method.

In addition, organosilicon compound orthosilicate [Si(OR) 4 ] or alkyl silicates [R 4-n Si(OR) n ] reacts violently with water, so adding in the sol stage will inevitably lead to waste of organosilicon compounds, SiO 2 The production cost of airgel increases, and the hydroxyl-OH is difficult to be completely replaced by hydrophobic groups. The product inevitably has hydrophilic problems. It is easy to absorb water during storage and transportation, resulting in performance degradation or even structural collapse. The product is scrapped

[0009] In addition, the incineration and carbonization of rice husk is a difficult process to control

Too low temperature may lead to incomplete carbonization and affect the purity of the product; slightly higher temperature or longer time may cause a large amount of ash, carbonaceous residue or metal residue to remain on the SiO 2 In the pores of the network porous structure, the extracted SiO 2 The highest content can only reach about 98%, and it can only be used for some industrial products and building materials that do not require high purity; increasing the temperature can oxidize impurities, but it cannot guarantee SiO 2 The form does not change from an amorphous state to a crystalline state and loses adsorption performance and destroys the porous network structure

In addition, the incineration process itself is a waste of heat energy, and it is difficult to avoid the release of environmentally harmful gases or smoke during the incineration process, causing environmental pollution and endangering human health.