Continuous Extraction Rate Measurements During Supercritical Carbon Dioxide Drying of Silica Alcogels.

摘要

Drying, specifically supercritical CO2 (SCCO2) -based drying, is a crucial step in the manufacture of silica aerogels and is also one of the most time and energy intensive. The aim of the present work is to elucidate the kinetics of this process in order to facilitate its acceleration. An apparatus was developed which is capable of continuously measuring ethanol extraction rates as a function of various process variables by three separate and redundant techniques. Results from experimental drying of 220 mm alcogel annuli (46 mm ID, 56 mm OD) are presented over a range of CO2 flow rates from 1 kg/hr to 5 kg/hr. A concentric annular model was developed which considers the conjugate mass transfer problem of diffusion within the alcogel, with composition dependent diffusivity, and convective flow over it. The model is shown to agree relatively well with experimental data.