Destabilized asphaltenes can easily adhere to the oil well production equipment, the transportation pipelines, and also the refining and storage facilities, resulting in significant remediation costs. Therefore, it is of great importance to the energy industry to understand the factors that govern the kinetics of asphaltene aggregation and precipitation. In this study, the effect of asphaltene concentration on their aggregation and precipitation tendencies after their destabilization with heptane is investigated for three different types of asphaltenes. It is intuitively expected that any increase in asphaltene concentration will accelerate the precipitation kinetics after heptane addition. For asphaltene concentrations below 1 wt % in toluene, this expected trend is indeed experimentally confirmed. However, for asphaltene concentrations above 1 wt %, an increase in concentration leads to slower aggregation instead. We believe that this counterintuitive decline in the aggregation rate is due to the stabilizing effect of stable or soluble asphaltenes. This effect has been overlooked in the existing aggregation models, and our research provides a better understanding of the factors controlling aggregation process. Accounting for the solubilizing effect of stable asphaltenes can provide successful predictions for the aggregation rate of asphaltenes at different asphaltene concentrations using Smoluchowski’s model.

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.