Apparatus to Measure Ethanol Extraction Rates During Supercritical Carbon Dioxide-Based Drying of Alcogels

An important and time consuming portion of the manufacturing of aerogel insulation is the supercritical carbon dioxide extraction step. An improved understanding of its kinetics is likely to reduce the time and energy required to dry alcogels and thus make aerogel insulation more economically feasible. A supercritical CO2 extraction apparatus was designed, constructed, and characterized. Then the rate of ethanol removal from a 220 mm tall x 46.2 mm inner diameter x 5 mm thick annulus of alcogel as a function of time was measured. Three independent techniques to track the mass fraction of ethanol in the effluent were considered. First, an IR-based sensor was used to directly measure it. Secondly, an equation of state for the CO2 + ethanol system to compute mass fraction of ethanol as a function of temperature, pressure and density was utilized to extract mass fraction from effluent densities measured by a Coriolis flowmeter. Lastly, the ethanol in the effluent stream was condensed into a graduated cylinder mounted on a laboratory scale. The apparatus allows for control of the thickness of the (annular geometry) channel for carbon dioxide flow surrounding the alcogel in addition to pressure, temperature, and mass flow rate of carbon dioxide. The experimental results highlight the impact of carbon dioxide mass flow rate on ethanol removal rate and overall drying time. The apparatus can be used to collect benchmark data for the extraction process and those data may then be compared to predictions from various models of the extraction process. Additionally, the rig was modified for density measurements of the CO2 + ethanol binary system as a function of mixture composition, temperature, and pressure in order to develop higher accuracy equations of state for the CO2 + ethanol system.