Cubic-Plus-Chain (CPC): A SAFT-Based Chain Modification to the Cubic Equation of State for Large Nonpolar Molecules

An equation of state framework for nonpolar chain molecules is proposed that hybridizes the classical cubic equation of state with the chain equation of state from SAFT. The cubic equation of state serves as the physical description of the monomer beads, providing repulsive and attractive character to the segments, and the chain term bonds these monomer segments to form chains of homogeneous beads. The CPC model molecule is a better representation of chain-like molecules, such as n-alkanes and polymers, and phase behavior modeling with the proposed CPC equation of state shows considerable improvement over the reference cubic equation of state. Additionally, CPC compares well to PC-SAFT in its description of both hydrocarbon VLE and polymer/solvent LLE despite being substantially less computationally expensive. The polymer/solvent example illustrates that a relatively simple modification can be made to the classical cubic equation of state that significantly improves density predictions while retaining many of the properties of the classical cubic equation of state that make it a popular model.