PC-SAFT modeling of asphaltene phase behavior in the presence of nonionic dispersants

Abstract

This study introduced a new method to characterize asphaltenes in PC-SAFT equation of state (EOS) and correctly model the effect of nonionic dispersants on the thermodynamic behavior of asphaltenes. Our approach is to combine microscale parameters from Molecular Dynamics (MD) simulations with Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) to develop a comprehensive model that enables the prediction of macroscopic behavior such as the amount and onset of asphaltene precipitation at various pressures, temperatures, and fluid compositions. More specifically, association parameters were considered for asphaltene molecules and determined by equating the Gibbs energy of association calculated by PC-SAFT EOS to the one obtained from MD simulations. A correlation was derived to relate the association energy parameter (ɛAB) of asphaltenes to the molar weight of their aromatic cores. Our model showed that asphaltene association energy is affected by temperature and solvent type and is inversely proportional to the solubility parameter of the medium. The hetero-segment approach in PC-SAFT EOS was adopted to accurately characterize asphaltene molecules and their non-association parameters in PC-SAFT were determined based on the molecular weight and aromaticity factor of asphaltenes. Moreover, the average aggregation number of asphaltene nanoaggregates was calculated using the Wertheim association theory. This model was applied to predict asphaltene precipitation envelopes for three different live crude oils and showed excellent agreement with experimental data in the literature. Additionally, the model could correctly predict the amount of asphaltene precipitation upon addition of nonionic dispersants.