A continuous production process for silica aerogel powders based on sodium silicate by fluidized bed drying of wet-gel slurry

The present study described a continuous process for the production of hydrophobic silica aerogel powders based on an inexpensive precursor such as sodium silicate. Fluidization technique was employed for the drying of wet-gel slurry at an ambient pressure. The fluidization column was fed with the silylated wet-gel slurry in a continuous mode and the fluidization was carried out at 220 degrees C. The aerogel powder collected in Trap-I was fluidized twice at room temperature in order to separate the lighter aerogel particles from the first trap. The tapping density of the aerogel powder decreased from 0.09 to 0.05 g/cm(3) for Trap-II, however, the microstructure did not differ significantly. Using this process, hydrophobic silica aerogel powders exhibiting tapping density as low as 0.05 g/cm(3), high specific surface area of 783 m(2)/g and cumulative pore volume of 1.79 cm(3)/g have been obtained. The aerogels were characterized by Field-Emission Scanning Electron Microscopy (FE-SEM), BET specific surface area, N-2 physisorption isotherms, pore size distribution and particle size analyses. The results have been compared with aerogel powders obtained by ambient pressure drying of the wet-gel slurry in a furnace. (C) 2008 Published by Elsevier Masson SAS.