Mesoscale Dissipative Particle Dynamics to Investigate Oil Asphaltenes and Sodium Naphthenates at the Oil−Water Interface

• Published in: Energy & fuels 2021-06, Vol.35 (11), p.9294-9311
• Main Authors: Ruiz-Morales, Yosadara, Alvarez-Ramírez, Fernando
• Format: Article
• Language: English
• Subjects: Fossil Fuels
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.1c00589

The effect of the structure of oil asphaltenes and sodium naphthenates at the oil–water interface on the reduction of the oil–water interfacial tension and the formation of stable emulsions is investigated by dissipative particle dynamics (DPD). The coarse-grained model molecules at the mesoscale level are adopted instead of using atomistic models. DPD can process a much larger spatial and temporal scale system than molecular dynamics (MD) can. Two types of island asphaltene model structures are used in the calculations: one with O atoms and the other one without O atoms. A small sodium naphthenate (benzoic acid sodium salt) is included in the simulations. The interfacial tension (IFT) is evaluated at different concentrations of sodium naphthenate while maintaining the asphaltene concentration fixed to conclude on the stability of the emulsions formed. The IFT results obtained for both asphaltene models are compared to reach conclusions regarding the relationships between asphaltene structure, surface activity and coverage, orientation at the oil–water interface, and stability of the emulsion formed by the asphaltenes and sodium naphthenates. Initially, when there is no sodium napthenates in the systems but only asphaltenes, the IFT decreases from 45 mN/m to 40 mN/m, because of the presence of asphaltene molecules at the oil−water interface. With the addition of sodium naphthenates to the systems, it is found that the asphaltene with no O atoms in the structure is less oil−water interface active and it is required to add a concentration of 0.363 M of sodium naphthenate to lower the IFT from 40 mN/m to 35 mN/m. The reduction of the IFT is mainly due to the formation of a uniform film of sodium naphthenates that covers the oil−water interface and displaces most of the asphaltenes with no heteroatoms to the oil region. This would explain why only