Mechanistic Insights into Polar Term Effects on PC-SAFT via Multiscale Simulation

The PC-SAFT model consists of hard-sphere, hard chain, dispersion, polarity, and association contributions. The influence of the polarity contribution on the predictive ability of the PC-SAFT model is evaluated from both microscopic and macroscopic perspectives. 27 representative polar substances are classified into four categories. Gaussian software is employed to simulate the molecular electrostatic potential （MESP） and molecular polarity index （MPI） for the 27 substances. The predictive capability of PPC-SAFT EoS with polarity terms and PC-SAFT EoS without polarity terms are evaluated with macroscopic properties, such as saturated vapor pressure, liquid density, and enthalpy of evaporation. The microscopic results of molecular simulation indicate that the polarity of the four categories decreases in the following order: aldehydes, ketones, chloroalkanes, and ethers. The polarity of the same type of substance decreases as the length of the carbon chain or the number of substituents increase. As the polarity decreases, the prediction results of macroscopic thermodynamic properties such as saturated vapor pressure by the PPC-SAFT and PC-SAFT models gradually close, and the contribution of the polarity effect weakens. The threshold values for MESP and MPI are determined to judge whether the PC-SAFT model should adopt the polar contribution terms according to the evaluation results. This conclusion can assist in avoiding unnecessary parameterization of complex systems and enhancing the computational efficiency in process simulations.