Estimating polystyrene equation of state (EOS) parameters using the cloud and critical points of polystyrene + hydrocarbon mixtures*

Abstract

Three polystyrene parameters for the modified Sanchez‐Lacombe equation of state were estimated by performing a correlation of the cloud and critical point data for six well defined polystyrene + hydrocarbon mixtures. The volume shift, a fourth parameter, was adjusted to the polystyrene pressure‐volume‐temperature (PVT) data. A parameterization of the modified Sanchez‐Lacombe equation of state is used to estimate the hydrocarbon parameters given their critical temperature, critical pressure, and acentric factor, but these properties are not available for the polymer. The original polystyrene parameters estimated solely on the pure component PVT data results have difficulty representing the slope and curvature of the cloud points of binary polystyrene + hydrocarbon mixtures. A previous technique for adjusting one of the polystyrene parameters to match the cloud points with the remainder fit to the PVT data results in an improved match over the pure component PVT data alone. Adjusting three polystyrene parameters can better match the cloud points of a binary polystyrene + hydrocarbon mixture, while only increasing the absolute average deviation in pure polystyrene density by 0.07%. The polystyrene parameters obtained by fitting the cloud points were used to correlate the bubble points of polystyrene in other solvents.

Issue Highlights

“…Usually, polystyrene parameters are adjusted solely to polystyrene pressure‐volume‐temperature (PVT) data; however, adjusting three PS parameters to match the binary mixture data and one PS parameter (the volume shift) to match the PVT data provides a qualitative representation of different types of phase behaviours. [ 4 ]…”