Molecular dynamics investigation of the asphaltene-kaolinite interactions in water, toluene, and water-toluene mixtures

Understanding the interactions of petroleum asphaltenes with mineral surfaces is important for diluted bitumen spill response and modeling. In this study, molecular dynamics and umbrella sampling simulations are performed using interfacially active and non-interfacially active asphaltene model compounds individually positioned near each of the surfaces of kaolinite in the presence of explicit solvent environments containing water, toluene, and mixtures of toluene and water in varying proportions. The interfacially active asphaltene bonds the strongest to the silicon oxide surface of kaolinite in pure water and the bonding weakens to nearly zero in toluene-water mixtures. The non-interfacially active asphaltenes bond to kaolinites silicon oxide surface in water about half as strongly as the interfacially active one in water and the bonding weakens in the presence of toluene. The number of non-hydrogen bonded contacts between the interfacially active asphaltene and the aluminum hydroxide surface of kaolinite increases as the proportion of toluene is increased and the contacts with water are decreased. In these conditions, the non-interfacially active asphaltenes do not form non-hydrogen bonded contacts with kaolinite. On the silicon oxide surface, the number of non-hydrogen bonded contacts of all asphaltenes with kaolinite tends to decrease as the proportion of toluene is increased and the contacts with water are decreased. The number of hydrogen bonds of the interfacially active asphaltene with water decreases as the proportion of toluene is increased. The radii of gyration indicate that the interfacially active asphaltene is extended in water and when adsorbed on kaolinite, and becomes compact as the proportion of toluene is increased. The simulation results highlight the competitive interfacial interactions in the complex scenario of diluted bitumen spills in the presence of water and clay minerals. (c) Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources Canada, 2022.

Automated summary

Understanding the interactions between petroleum asphaltenes and mineral surfaces is crucial for responding to diluted bitumen spills and modeling. This study employed molecular dynamics and umbrella sampling simulations to investigate the behavior of interfacially active and non-interfacially active asphaltene model compounds near kaolinite surfaces in different solvent environments. The simulations revealed that interfacially active asphaltenes form strong bonds with the silicon oxide surface of kaolinite in water, but the bonding weakens in toluene-water mixtures. On the other hand, non-interfacially active asphaltenes exhibit weaker bonding with kaolinite and do not form non-hydrogen bonded contacts. The results also indicated that the interfacially active asphaltene becomes more compact when the proportion of toluene increases. These findings provide valuable insights into the complex interfacial interactions during diluted bitumen spills in the presence of water and clay minerals.