Computational Study of Asphaltene Adsorption on Carbonate Surface: Role of Molecular Structure and Oil Phase

Asphaltene deposition on mineral surfaces poses significant challenges for the oil industry, impacting the extraction efficiency of fluids, affecting rock wettability, and causing formation damage. The presence of these heavy molecules in crude oil also causes the fouling of equipment and catalyst deactivation. Therefore, the molecular-level understanding of the asphaltene molecules (AM)–surface interactions is crucial in designing novel, site-specific chemical agents for asphaltene removal. In this study, we used molecular dynamics simulations to investigate the adsorption behavior of five different AMs (both island- and archipelago-type) on the calcite surface in a dodecane solvent. Using umbrella sampling, we obtained the potential of mean force of AMs, calculated the adsorption–desorption barriers, and performed structural and energetic analysis in detail. In contrast to common observation, we found that not all AMs exhibit preferential adsorption on the surface; instead, the AM with phenolic and pyrrolic functional groups were only found to adsorb, while those with thiophenic and quinoline functional groups faced barriers to adsorption. AM preferentially adsorbs over the calcium ions of the surface, facilitated by the strong heteroatom–surface interactions and supported by the hydrogen bond interactions. Further, the AMs compete with the solvent molecules for adsorption onto the surface, and those AMs that have a higher effective configurational energy get adsorbed. The interaction energy of AMs with the system is independent of the aromatic size, polarity-dependent on heteroatom, and linearly dependent on the aliphatic size. These detailed insights into the role of various parts of AM in its adsorption onto the mineral surface will facilitate the design of solvents and sorbents for effective asphaltene removal.