Thermodynamic models for asphaltene solubility and precipitation

A number of different models that have been applied to modeling of asphaltene precipitation and estimating asphaltene solubility in various systems are critically reviewed. Particular attention is paid to the basic assumptions and the performance of the models as compared to the present knowledge of composition and phase equilibrium of asphaltenes. In all models a number of parameters are tuned to obtain best fits to the experimental data. The main parameter was, as proposed in the reviewed works, the molecular weight of the asphaltene and only a few models take the aggregating nature of the asphaltenes into account. Even though the models are based on thermodynamic concepts, they remain empirical because of the number of parameters used in the calculations. When the solubility parameter is employed as the basis for a model, the calculation of asphaltene solubility cannot be calculated or estimated without extensive modification to the model. In summary, the models employed for predictability of asphaltenes precipitation are lacking in several respects and are not quantitatively accurate.