Multiphase Behavior in Ternary Mixtures of CO₂, H₂O, and Nonionic Amphiphiles at Elevated Pressures

Equilibrium multiphase behavior for ternary mixtures of carbon dioxide and water with 2-butoxyethanol (C4Ei) and with n-octyl tri(oxyethylene) monoether (C8E3) has been studied at temperatures and pressures near the critical point of C02. Four-phase liquid-liquid-liquid-gas equilibrium and threephase liquid-liquid-gas and liquid-liquid-liquid equilibria were observed for both ternary mixtures. Phase compositions and densities for three- and four-phase equilibria were measured at temperatures from 30 to 50°C and pressures from 615 to 1415 psia. Critical end point temperatures and pressures which bound the regions of multiphase equilibria were also measured, and tricritical points were estimated by the intersection of the critical end point curves. Dye solubilization experiments were performed to investigate the existence of micelles or reverse micelles in the equilibrium phases of these ternary mixtures. No evidence for the formation of micelles or reverse micelles was found.