Phase behavior studies of a perfluoropolyether in high-pressure carbon dioxide

This work presents vapor-liquid equilibrium measurements for the binary system carbon dioxide-Krytox 157 FSL, a commercial perfluoropolyether carboxylic acid terminated. The measurements were carried out between 313.15 and 343.15 K and at pressures up to 18 MPa in a static analytical apparatus. Krytox showed high miscibility with CO2 and it was possible to define the contour of the vapor-liquid equilibrium region as well the determination of the critical line. The Sanchez-Lacombe EOS was able to calculate the liquid equilibrium composition of the CO2 + Krytox binary system quite adequately, by fitting two temperature dependent interaction parameters, although it did not predict any solubility for the vapor phase. Due to lack of thermodynamic data, the characteristic parameters of Krytox were estimated by a method proposed by Sanchez and Lacombe, using a known heat of vaporization, a vapor pressure and a liquid specific volume at 313 K.