A PC-SAFT model for hydrocarbons III: Phantom dipole representation of dipole induced dipole interactions in unsaturated hydrocarbons

Abstract

Inclusion of polar contributions into the statistical associating fluid theory class of equations of state has been demonstrated to allow for the accurate prediction of solution non-idealities of mixtures composed of paraffins and polar molecules. However, as we demonstrate in this paper, these theories necessarily overpredict the non-idealities in mixtures composed of polar molecules with unsaturated hydrocarbons. The reason for this is that the dipole moment of the polar molecule polarizes the unsaturated bond resulting in a significant dipole-induced dipole attraction. We develop a simple, general and predictive methodology to incorporate this missing physics into the dipolar contribution to the theory. The new approach is shown to accurately predict the phase behavior of unsaturated hydrocarbons with polar molecules.