HIGH-PRESSURE PHASE-EQUILIBRIA OF POLY(ETHYLENE GLYCOL) CARBON-DIOXIDE SYSTEMS

Phase equilibrium data of different molecular weight poly(ethylene glycol)-CO2 mixtures are presented and correlated by using a lattice-model-based equation of state. The data were obtained at 313 and 323 K over a pressure range up to 29 MPa. Typical temperature, pressure, and molecular weight dependences of the solubility data are discussed. The model correlates the data quantitatively by using a single adjustable parameter, kij, in a modified mixing rule for the interaction energy of the mixtures. A finite lattice coordination number, z = 10, and a constant lattice site volume, vH = 9.75 × 10-6 m3/mol, are used, and the sensitivity of the model to the assumed values of z and vH are discussed. Although other investigators have previously applied lattice models to supercritical systems, in this study the lattice model has been applied to a more challenging case where the solvent dissolves appreciably in the polymer and hence the supercritical phase is no longer in equilibrium with a pure solute. This is accomplished with a single adjustable parameter. © 1990 American Chemical Society.