Interfacial Tension and Density of Ethanol in Contact with Carbon Dioxide

Abstract

The interfacial tension of ethanol in contact with carbon dioxide is measured at temperatures between 20 and 80°C and at pressures between 1 and 105 bar. The interfacial tension decreases with increasing pressure. After 5 seconds the time dependency of the interfacial tension of ethanol in contact with carbon dioxide is negligible because of the fast mass transfer of carbon dioxide into ethanol. The dissolution of carbon dioxide at lower pressure leads to a distinct rise in the density of ethanol. The carbon dioxide saturated ethanol density reaches a maximum at a certain pressure. It decreases steadily if the pressure continues to increase until the system ethanol and carbon dioxide has become a single-phase. Comparing the interfacial tension of ethanol, water and of ethanol-water mixtures, one realizes that the interfacial tension increases with descending ethanol concentration. During a countercurrent extraction of an ethanol-water mixture the extraction of ethanol leads to a rising interfacial tension, while during a countercurrent extraction of e.g. triglycerides the interfacial tension decreases due to the dissolution of carbon dioxide. One implication of the results is that comparing the mass transport of trigylcerides into carbon dioxide with the mass transfer of ethanol into carbon dioxide, one has to consider the following: the interfacial tension is rising with falling ethanol concentration. This could lead to a different mass transfer due to Marangoni convection.