DIFFUSION OF ETHANOL CARBON-DIOXIDE IN SILICA-GEL

Extraction of a primary solvent with liquid or supercritical carbon di oxide is the most difficult to control stage in low-temperature silica aerogel production. Diffusion of primary ethanol through alcogel stru cture to surrounding CO2 was investigated in carefully controlled expe riments with cylindrical alcogel samples. Changes of the alcohol conce ntration in carbon dioxide leaving the autoclave were followed with on -line chromatograph analysis and experiments were repeated for tempera tures around the critical point of carbon dioxide. On the basis of the concentration histories during the drying, the temperature dependence of diffusion coefficient in the ethanol-CO2 mixture inside the silica gel at constant pressure was identified. (C) 1998 Elsevier Science B. V. All rights reserved.