Solubility of benzyl methacrylate/methacrylic acid copolymers in carbon dioxide-expanded acetone and correlation with the PC-SAFT equation of state

The high-pressure solid–liquid–vapor phase behavior of ternary systems comprising CO2, acetone, and benzyl methacrylate (BzMA)/methacrylic acid (MAA) copolymers has been probed experimentally and modeled with the PC-SAFT equation of state. Precipitation of BzMA/MAA copolymers required a larger overall CO2 mole fraction – and a correspondingly higher system pressure – in dilute solutions; however, a minimum in the precipitation pressure was observed for all copolymer compositions and temperatures near a CO2-free copolymer mass fraction of 0.05. These systems were characterized by a rapid reduction in copolymer solubility over a relatively narrow range of pressure (between 1.48 MPa and 2.86 MPa). The precipitation pressure increased with increasing temperature and BzMA mass fraction (per copolymer mass unit). The PC-SAFT EOS was successfully used to correlate the phase behavior data using binary interaction parameters with linear temperature dependence. The average relative error associated with the calculated precipitation pressure for each copolymer was 4.1% over the range of temperature and composition examined. Liquid phase carbon dioxide mole fraction was calculated to monotonically increase with increasing solid precipitation pressure, implying that carbon dioxide does not act as an antisolvent at higher (>5 wt%) copolymer fractions.