Effect of cooling rates on aggregation interaction of asphaltene molecules: Insights from molecular dynamics simulations

Abstract

Understanding the behavior of asphaltene molecules and their aggregation processes is essential to optimize the performance of crude oil transport pipelines. However, the effect of cooling rate on asphaltene aggregation behavior has rarely been studied. To this end, this study conducted an investigation using molecular dynamics simulations to elucidate the influence of cooling rates on the aggregation degree, microscopic behavior, and underlying mechanisms of C5Pe asphaltene molecules from the configuration evolution, gyration radius, radial distribution function (RDF), cluster size distribution, number of clusters, and diffusion coefficients. Results show that asphaltene molecules exhibit two primary aggregation modes: nucleation aggregation and coalescence aggregation. Under slower cooling rates, asphaltene molecules exhibit nucleation aggregation behavior, where certain molecules aggregate into compact nuclei, followed by the accumulation of additional asphaltene molecules around these nuclei. In contrast, faster cooling rates induce coalescence aggregation, whereby asphaltene molecules initially form multiple small aggregates that subsequently merge into larger structures as the temperature decreases. These findings contribute to understand the kinetic characteristics of asphaltene aggregation and the complexity of aggregation mechanism, and provide theoretical support for the flow assurance of pipeline transportation of crude oil.