Apparatus to measure density and viscosity of high-pressure carbon dioxide-alcohol mixtures

Thermophysical properties of (single phase) binary CO2-alcohol mixtures under high pressure and moderate temperature conditions are important in supercritical fluid processes. An apparatus to measure mixture density as a function of temperature (up to 80 °C) and pressure (up to 15.9 MPa) over the full range of CO2 mass fractions was designed and commissioned. The fluid delivery system enables precise control and rapid variation of the CO2 mass fraction to within 0.2% of the desired value. Our apparatus advances the state-of-the-art by assuring a uniform mixture and assuring accuracy through redundant measurements, i.e., a variable-volume method with an uncertainty of 1% of reading and a Coriolis density meter with an uncertainty of 7 kg/m3. The results for a representative CO2-ethanol mixture are provided. Moreover, a third independent "bomb" experiment was used to measure density under selected conditions to further verify our measurements and, when present, discrepancies between them and the published data for the representative system. It is shown that, when the discrepancies were present, it was due to insufficient mixing in the other apparatus. Our apparatus also measures the viscosities of the mixtures using a viscometer accurate to 0.02 cP.