Investigation of clay-oil interfacial interactions in petroleum-contaminated soil: Effect of crude oil composition

Abstract

Crude oil, a multi-component complex organic aggregate, causes petroleum-contaminated soil (PCS) with complex properties, which makes PCS unable to achieve rapid and effective oil-soil separation. Therefore, it is crucial to investigate the impact of different crude oil components on oil-soil interactions in PCS. In this study, crude oil was divided into SARA, saturates (S), aromatic (Ar), resin (R) and asphaltene (As) in accordance with polarity and solubility to explore their thermal desorption and thermal variation of adsorption on the kaolinite (Kln) surface. Moreover, the detailed sources of the interactions were investigated using the oil-clay interfacial free energies and interfacial forces. Furthermore, molecular dynamics (MD) simulations were performed to gain insight into the interfacial interaction mechanisms. The results indicated that the polarity of SARA components followed an order of As > R > Ar > S, and the temperature required for thermal desorption and the heat released during oil-clay adsorption increased with an increase in polarity. The van der Waals forces dominated oil-clay interactions. The benzene ring and heteroatom (N, O, and S) in the polar components facilitated the oil-clay van der Waals interactions. Besides van der Waals, the higher number of benzene rings led to the generation of electrostatic interactions as well as hydrogen bonding between heteroatoms and the –OH of Kln, thus increasing the free energy and force at the oil-clay interface. The result of MD was consistent with the experimental results, thus suggesting that van der Waals, electrostatic forces, and hydrogen bonds reliably exist during the interaction between polar oil molecules and clay. Simultaneously, the oil-clay binding energies increased with higher polarity. These findings provide guidance on developing advanced oil-clay separation processes.