Asphaltenes Flocculation: Coarse-Grained Simulations

Abstract

There are significant barriers to successfully simulating asphaltene precipitation behavior. First, the accurate representation of specific asphaltenes is challenging due to their intrinsic complexity, and second, the size of the systems can limit the analysis of the temporal evolution to a few tens of nanoseconds when atomistic simulations are used. We present an approach to overcome these two barriers by integrating asphaltene mixtures built to match average properties with coarse-grained simulations. The asphaltene behavior is studied as toluene is replaced by n-heptane in a stepwise fashion, resembling the asphaltene titration. Three different asphaltene model mixtures (virgin Asphaltenes A1 and A2 and processed Asphaltenes B) were built to match the average properties of real asphaltenes. The results showed that coarse-grained simulations allowed longer run times and length scales than previous atomistic modeling, extending from a few nanoseconds to an equivalent of 0.75 μs. Additionally, numerical calculations captured the impact of changes in the asphaltene aggregation mechanisms. Specifically, the virgin materials showed an overall lower aggregation percentage and lower cluster formation (monomer, dimer, and trimer) with varying shapes. Conversely, the processed asphaltenes showed a 7-fold increase in aggregation percentage through π–π stacking via their large aromatic cores. Compared with Turbiscan precipitation experiments, our simulations showed good qualitative alignment for both virgin asphaltene A1 and processed asphaltene B. Significant deviations are observed for virgin asphaltene A2, which is attributed to the difference in heteroatomic functional groups. These findings highlight the critical influence of heteroatomic functionalities on asphaltene aggregation behavior and emphasize that reliable molecular characterization data is essential for developing simulations that accurately match experimental observations.