INTERFACIAL-TENSION IN HIGH-PRESSURE CARBON-DIOXIDE MIXTURES

Interfacial tensions of carbon dioxide-water-alcohol mixtures were measured at temperatures in the range 5-71 degrees C and pressures 0.1-18.6 MPa, using the capillary rise method. The alcohols were methanol(0.136 mf), ethanol (to 0.523 mf), and isopropyl alcohol (to 0.226 mf). Interfacial tension (IFT) decreased linearly with both temperature and pressure in the low-pressure range (gaseous CO2) but was largely independent of pressure at high pressure (liquid or supercritical CO2). There was a zone in the vicinity of the critical pressure of CO2-as much as 20 degrees C below and 10 degrees C above the carbon dioxide critical temperature-where IFT became small. This is attributed to the formation of a second CO2-rich phase. The isotherms exhibited a crossover pressure near 3 MPa for all systems examined.