Phase Equilibrium for Surfactant Ls-54 in Liquid CO2 with Water and Solubility Estimation

It is known that the commercial surfactant Dehypon® Ls-54 is soluble in supercritical CO2 and that it enables formation of water-in-CO2 microemulsions. In this work we measured phase equilibrium in the Ls-54/CO2 and Ls-54/water/CO2 systems in the liquid CO2 region, from 278.15 - 298.15 K. Ls-54 in CO2 can have solubilities as high as 0.086 M at 278.15 K and 15.2 MPa. The stability of the microemulsion decreases with increasing concentration of water, and lower temperatures favor increased solubility of water into the one-phase microemulsion. In addition, the Peng-Robinson equation of state (PREOS) was used to model the phase behavior of Ls-54/CO2 binary system as well as to estimate water solubilities in CO2. The PREOS model showed satisfactory agreement with the experimental data for both Ls-54/CO2 and water/CO2 systems.