Effect of CO2 on the Interfacial and Transport Properties of Water/Binary and Asphaltenic Oils: Insights from Molecular Dynamics

We conducted molecular dynamics (MD) simulations to investigate the effect of supercritical carbon dioxide (sc-CO2) on the interfacial and transport properties of water-oil systems. The oil phase was resembled by employing different binary hydrocarbons (paraffin + aromatic), namely, benzene + hexane, benzene + octane, xylene + hexane, and xylene + octane. Furthermore, we added an asphaltene to the system composed of xylene and hexane to study the interfacial behavior of the heaviest fraction of oil (asphaltene) in the presence of CO2. The simulations were performed under the operating conditions of 100 bar and 350 K. The results showed that aromatics, CO2, and asphaltenes accumulated at the interface at low CO2 mole fractions (x(CO2)). However, when x(CO2) increased, it displaced the aromatics away from the interface and toward the bulk. At very high x(CO2) the aromatics accumulated at the oil bulk. Similarly, asphaltene molecules stacked at the interface at low x(CO2) and as x(CO2) increased, some of the asphaltene molecules dissolved and aggregated in the oil bulk. CO2 forms a film between water and oil phases, and as the thickness of the film increases, it displaces the hydrocarbons away from the interface. The addition of sc-CO2 diluted the interface, formed hydrogen bonds (H bonds) with water, which stabilize the CO2 film, and reduced the interfacial tension in all systems. Furthermore, the addition of sc-CO2 increased the diffusivity of the oil phase in all systems. However, it significantly affected the diffusivity of systems that have less polar aromatics.