An equation-of-state contribution for polar components: Dipolar molecules

Accounting for dipolar interactions in a physically based equation of state (EOS) can substantially improve the modeling of phase equilibria of real mixtures. An EOS contribution for dipolar interactions of nonspherical molecules is developed based on a third-order perturbation theory. Molecular simulation data for vapor-liquid equilibria of the two-center Lennard-Jones (2CLJ) plus pointdipole fluid is used to determine model constants of the EOS. The resulting model is compared to simulation data of pure dipolar nonspherical molecules and their mixtures and an excellent agreement is found. The proposed dipole term is applied to real substances with the perturbed-chain statistical associating fluid theory (PC-SAFT) EOS and it is confirmed that accounting for dipolar interactions not only reduces the binary interaction parameter, but also improves the description of pure component and mixture phase equilibria. Literature values for the dipole moment can thereby be used and no further dipole-related pure component parameter has to be adjusted. This constitutes an advantage over earlier approaches, where dipole-related parameters were fitted to pure component data or to mixture data. (c) 2005 American Institute of Chemical Engineers.