Effect of Inhibitors on Asphaltene Aggregation: A Theoretical Framework

The effect of inhibitors in asphaltene aggregation is studied using a molecular thermodynamic approach. In the proposed model, inhibitors interact with active sites in the core of the asphaltene aggregates and their energetic contributions to the formation of an aggregate inhibitor complex are taken into account. The incorporation of inhibitors induces changes in the free energy contributions to the formation of the asphaltene aggregates. In particular, it affects the interactions between solvent and aggregates and induces new steric interactions in what can be considered as the aliphatic crown of the aggregates. When the model included specific factors related to asphaltene and inhibitor characteristics, it allowed for the rationalization of different experimental behaviors observed for asphaltene inhibitor solutions, such as the effect of the molecular structure of inhibitors, asphaltene characteristics, and solvent-related issues, such as inhibitor solubility and self-aggregation. According to the model, inhibitors can significantly reduce the number of asphaltenes per aggregate. However, this does not mean that aggregates become smaller. Dependent upon several factors, the resulting aggregates can be on average smaller, the same size, or even larger than the original asphaltene aggregates. The model also indicates the existence of an optimal inhibitor concentration for each system.