Interfacial tension in high-pressure carbon dioxide mixtures

High-pressure interfacial- and surface-tension phenomena govern the migration and recovery of oil and gas from hydrocarbon reservoirs. The phenomena are of particular relevance to phase separation and mass transfer in light hydrocarbon fractionation plants and in propane deasphalting in lubricating oil refining. Interfacial tensions of carbon dioxide-water-alcohol mixtures were measured at temperatures in the range 5--71 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 din the low-pressure range (gaseous CO{sub 2}) but was largely independent of pressure at high pressure (liquid or supercritical CO{sub 2}). There was a zone in the vicinity of the critical pressure of CO{sub 2}-as much as 20 C below and 10 C above the carbon dioxide critical temperature--where IFT became small. This is attributed to the formation of a second CO{sub 2}-rich phase. The isotherms exhibited a crossover pressure near 3 MPa for all systems examined.