(553i) A Novel Approach to Include Double and Triple Bond Polarization in Unsaturated Hydrocarbons By Polar Solvents in an Equation of State

Extractive distillation processes to separate close boiling mixtures of alkanes, alkenes and alkynes rely on the introduction polar solvents for which hydrocarbon solubility increases with the degree of unsaturation. 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 (k_ij = 0) the phase behavior of unsaturated hydrocarbons with polar molecules. This new predictive approach allows for accurate process simulations and solvent selection in extractive distillation processes without the need of an extensive amount of experimental binary VLE data to tune the model.