The precipitation of asphaltenes from crude oils can lead to serious challenges during oil production and processing. This research investigates the kinetics of asphaltene precipitation from crude oils using n-alkane precipitant. For several decades, it has been understood that the precipitation of asphaltenes is a solubility-driven phenomenon, and the previous studies on the effect of time are usually limited to short time scales. By using optical microscopy and centrifugation-based separation, we have demonstrated that the time required to precipitate asphaltenes can actually vary from a few minutes to several months, depending on the precipitant concentration used. Our results demonstrate that no single concentration can be identified as the critical precipitant concentration for asphaltene precipitation. On the basis of long-term experiments, we have also been able to establish the solubility of asphaltenes as a function of the precipitant concentration, and it is shown that the short-term experiments overpredict the solubility. Similarities between the current work and other research areas are also discussed briefly. This research opens up a new paradigm for understanding asphaltene precipitation.

The effect of different n-alkane precipitants on the kinetics of asphaltene aggregation is investigated in this study. When the chain length of the n-alkane precipitant, i.e., the carbon number, is increased, both the viscosity and solubility parameter of the solution increase and, as a result, the aggregation rate is expected to decrease. However, the actual behavior of the system is more subtle, and the aggregation rate can remain constant, increase, or pass through a maximum as the carbon number, n, increases. This behavior can be explained by the polydispersity of asphaltenes and the weaker precipitating power of longer chain n-alkanes. The polidispersity of asphaltenes is successfully characterized using their solubility parameter and the model developed in our previous study (Haji-AkbariN.MasirisukP.HoepfnerM. P.FoglerH. S. Haji-Akbari, N. Masirisuk, P. Hoepfner, M. P. Fogler, H. S. Energy Fuels20132724972505), where a universal relationship between the detection time and the differences in solubility parameters was established. The solubility parameter of the precipitated asphaltenes is shown to increase with increasing the chain length of the n-alkane precipitants and is successfully used to predict the aggregation rate of asphaltenes in blends of up to five different n-alkane precipitants.