High pressure phase equilibria for poly(ethylene glycol)s + CO2:: experimental results and modelling

Phase equilibrium results for mixtures of three poly(ethylene glycol)s (PEGs) of molar mass 200, 400 and 600 g mol(-1) with carbon dioxide over the temperature range 313.15-348.15 K and pressures up to 26 MPa are presented. A new static analytical apparatus was built to carry out these measurements. The precision of the method is better than 3% and the accuracy is estimated to be better than 5% of the mass fraction. The results are well correlated with the Sanchez-Lacombe equation of state, using a non-temperature dependent interaction parameter zeta. Negative hydroxy end-group effects on the CO2 solubility in the polymer are highlighted in the case of PEG 200. Data from other workers for CO2 + heavier PEG (1500-8000 g mol(-1)) are also successfully included in the correlation. However, previously published values for PEG 400 to PEG 1000 differ substantially from our results and could not be simultaneously correlated by this model.