Effect of specific interaction of CO2 with poly(ethylene glycol) on phase behavior

Abstract

The specific interaction (i.e., Lewis acid-base interaction) between CO2 and the ether group in poly(ethylene glycol) (PEG) is expected to significantly affect the mutual solubility in CO2/PEG systems. Therefore, in order to understand the liquid-liquid equilibrium (LLE) phase behavior under supercritical CO2, the specific intermolecular interaction between CO2 and PEG should be involved in the theoretical modeling of LLE phase behavior for the PEG/CO2 system. In this work, this interaction (i.e., CO2-PEG complex due to the Lewis acid-base interaction) is treated by the perturbed-chain SAFT (PC-SAFT) model as a cross-association between CO2 and PEG. The cross-association energy parameter is estimated from the experimental enthalpy by the Fourier transform IR (FT-IR) spectroscopy method for CO2 and the ether group in PEG. The correlated pressure and temperature (P-T) isopleth curve with the cross-association between CO2 and PEG is much closer to the experimental data. The degree of cross-association decreases as the temperature increases. This strong cross-association leads to a lower critical solution temperature (LCST) phase behavior, even at supercritical conditions.