Cubic-Plus-Chain (CPC). I: A Statistical Associating Fluid Theory-Based Chain Modification to the Cubic Equation of State for Large Nonpolar Molecules

Abstract

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 (Chapman et al., Fluid Phase Equilibria, 1989). 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. Whereas the model molecule of the standard cubic equation of state is a sphere with variable attraction energy and volume but whose fundamental shape remains roughly spherical, the model molecule of the proposed cubic-plus-chain (CPC) equation of state consists of beads bonded covalently to form linear chains. 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, mainly du...