Continuous extraction rate measurements during supercritical CO2 drying of silica alcogel

• Published in: The Journal of supercritical fluids Vol. 94; pp. 38 - 47
• Main Authors: Griffin, Justin S., Mills, Drew H., Cleary, Martin, Nelson, Ryan, Manno, Vincent P., Hodes, Marc
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2014
• Subjects: Aerogel; Modeling; Supercritical CO2 drying; Aerogel; Modeling; Supercritical CO2 drying
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2014.05.020

[Display omitted] •A new apparatus has been developed which continuously measures the alcohol extraction rate during supercritical CO2=based drying of silica alcogels.•Extraction is shown to be largely diffusion limited, except at low CO2 flow rates.•A model of the process which considers a composition-dependent diffusivity is shown to be in good agreement with experimental results.•Use of mixture density as a metric by which to measure drying progress is shown to have great potential for integrating into industrial aerogel production systems. We investigated the kinetics of supercritical CO2 (SCCO2)-based drying of silica aerogels, a common, but time consuming and energy intensive step in their manufacture. An apparatus was developed to continuously measure alcohol extraction rates from alcogels as a function of key process variables by two redundant techniques. Kinetics data are reported for the drying of 2.5mm, 5mm, and 7.5mm thick annular alcogels by pumping SCCO2 through a 10mm-thick concentric annulus surrounding their exterior. The SCCO2 was at a temperature of 323K and a pressure of 12.4MPa and its mass flow rate varied from 1kg/h to 5kg/h. Gel thickness and SCCO2 flow rate were both shown to significantly effect drying rate and required drying time. The results of a conjugate mass transfer model assuming pure diffusion in the alcogel compared favorably with the data when the composition dependence of molecular diffusivity was captured utilizing available correlations.