Development Of Silica Aerogel Production Technology

Silica aerogel has potential applications in wide areas due to its specific properties,for example,it has been used as a super thermal insulation material.It can also be used as the matting agent,catalyst,carriers for catalyst,flavors and fragrances,food,and so on,but the uses have been limited due to the technical and cost problems.The production of silica powders with sodium silicate has been an economic route,however,the normal product of silica has poor performance,and even worse,it causes large sewage discharge,leading to big environmental problem.In this study,on the basis of our group 's previous investigation of a batch high pressure carbonation process and supercritical drying(both batch and continuous processes),we proposed a continuous high pressure carbonation process and a novel continuous supercritical drying process for producing silica aerogel to resolve the mentioned existing problems.By using the sodium silicate as the raw material,a continuous high pressure carbonation process was proposed and established.The operation parameters such as the solution concentration,reaction pressure and pressure difference,nozzle size,aging pressure and so on were investigated to find the effect on the silica aerogel properties like specific surface area,pore size and pore volume.Results showed that when the concentration of solution was 0.75 mol/L,the pore volume as high as 5.2 cm3/g could be achieved.The recovery of the side product sodium hydrogen carbonate was investigated to use it as a raw material to produce sodium silicate with quartz sand.Through the research,we found the preliminary washing parameters:the sodium silicate modulus of 3.5,concentration of 0.75 mol/L(it not only kept the quality of silica product but also reduced the consumption of water),preheat of the hydrogel at 70 ? for 0.5 h,and washing four times.With the use of the filtrate from the recovery process,a continuous supercritical drying process was proposed and established.The device showed high production efficiency,product stability,and easy scale up.Finally,the product was used as a matting agent;a new index was also proposed for characterizing the transparence.Results showed excellent extinction index(80.67%)and transparence index(87.70%).This work,through the systematic studies of the whole process,including the reaction,side product recovery,and product drying,and two typical novel designs in reaction and drying,realized an environmentally friendly production technology for silica aerogel.This provides the foundation for an industry scale production process.