The influence of carbon dioxide cosolvent on solubility in poly(ethylene glycol)

Supercritical carbon dioxide (CO2) and poly(ethylene glycol) (PEG) can be utilized as an environmentally friendly biphasic solvent system for catalysis reactions and subsequent product separation. To efficiently implement this technology, it is important to understand how solutes partition between these phases as well as how dissolved CO2 in PEG affects the solvent properties. The work presented here explores the influence of CO2 on the solubility of four different solutes in PEG. The transferable potentials for phase equilibria-united atom force field and configurational-bias Monte Carlo molecular simulation were employed to determine the solubilities of ethylbenzene, 1-octene, 1-pentanol, and 2-pentanone at 323.15 K and 15 MPa in PEG-600 using an ideal vapor phase with a Poynting-corrected vapor pressure. The effect of CO2 concentration within the PEG phase was determined by varying the amount from no CO2 to the saturation limit. The results indicate that while there is preferential solvation of CO2 around the solutes, solubility of non-polar solutes is unchanged whereas there is a modest increase for polar solutes as the concentration of CO2 increases. Increased solubility is analyzed in terms of both modified solvent structure and direct solute-CO2 interactions.