Cubic-Plus-Chain III: Modeling Polymer-Solvent Phase Behavior with the Chain-Modified Cubic Equation of State

The cubic-plus-chain (CPC) equation of state (Sisco & Abutaqiya et al., Ind. Eng. Chem. Res., 2019) is a recent development in the literature in which the classical cubic equation of state is hybridized with the chain term from the statistical associating fluid theory (SAFT) to produce an equation of state capable of describing the shape and interaction energy of nonpolar chainlike molecules. In this work, the CPC framework is used to model vapor-liquid and liquid-liquid phase equilibria for various polymer-solvent systems. Polypropylene, high-density polyethylene, low-density polyethylene, and polystyrene polymers are modeled with various nonpolar solvents, and various factors-including temperature, solvent character, polymer molecular weight, and concentration-are investigated to study their effects on the saturation points predicted by the CPC equation of state. The modeling results from CPC are compared to those generated using the perturbed-chain SAFT (PC-SAFT) equation of state and also the experimental data reported in the literature. Though the predictive capability of CPC is not yet on par with PC-SAFT, it is impressive that this conceptually simple framework can qualitatively describe polymer phase behavior while retaining the numerical stability and fast execution times that make the cubic equations of state appealing.