A Thermodynamic Mixed-Solid Asphaltene Precipitation Model

A simple model for the prediction of asphaltene precipitation is proposed. The model is based on an equation of state and uses standard thermodynamics, thus assuming that the precipitation phenomenon is a reversible process. The solid phase is treated as an ideal multicomponent mixture. An activity coefficient model based on the athermal Flory-Huggins expression was included to account for solid phase non-ideality, but was found to have little effect on the results. Only a fraction of each of the heaviest components are considered potentially solid forming. This approach is based on the assumption, that out of the total PNA composition of a crude, the asphaltenes and resins are mainly aromatic-naphtenic in their nature. The predictions shows the correct qualitative behavior with respect to temperature and pressure, but due to lack of data the model was not evaluated quantitatively with respect to these effects.