Structural Behavior of Isolated Asphaltene Molecules at the Oil–Water Interface

Abstract

Asphaltenes are the heaviest component of crude oil, causing the formation of a stable oil−water emulsion. Even though asphaltenes are known to behave as an emulsifying agent for emulsion formation, their arrangement at the oil−water interface is poorly understood. We investigated the effect of asphaltene structure (island type vs archipelago type) and heteroatom type (Oxygen-O, Nitrogen-N, and Sulfur-S) on their structural behavior in the oil−water system. Out of six asphaltenes studied here, only three asphaltenes remain at the oil−water interface while others are soluble in the oil phase. Molecular orientation of asphaltene at the interface, position, and angle of asphaltene with the interface has also been determined. We observed that the N-based island type asphaltene is parallel, while the O-based island type asphaltene and Nbased archipelago type are perpendicular to the interface. These asphaltene molecules are anchored at the interface by the heteroatom. The S-based asphaltenes (both island and archipelago type) and O-based archipelago type asphaltenes are soluble in the oil phase due to their inability to form a hydrogen bond with water and steric crowding near the heteroatom. This study will help in understanding the role of asphaltenes in oil−water emulsion formation based on its structure and how to avoid it.

Investigation of Adhesion between Heavy Oil/Bitumen and Reservoir Rock: A Molecular Dynamics Study

“…The 1–4 non-bonded interactions of heavy oil molecules were scaled by 0.5 as per the OPLS-AA force field. , The calcite, silica, and mica surface of the reservoir rock were modeled using the force fields of Xiao et al, Lee and Rossky, and CLAYFF, respectively. These force fields have been used in previous work and have been shown to reproduce the properties of their respective systems in agreement with experimental data. , They have also been used to study heavy oil molecules at oil–water and oil–rock interfaces. , …”

“…24,39 They have also been used to study heavy oil molecules at oil−water and oil−rock interfaces. 40,41 2.4. Simulation Details.…”

Toward Predictive Molecular Dynamics Simulations of Asphaltenes in Toluene and Heptane

“…26 Therefore, following the studies of Mullins 1 and Li and Greenfield, 54 we considered an asphaltene molecule with the “typical” chemical structure shown in Figure 9, which has been successfully used in the past to describe the structure of asphalt 55−57 and the water–oil interface. 58 This asphaltene model has a molecular weight of 707.1 g/mol. It contains seven aromatic rings, several long and short linear aliphatic side groups, and one sulfur heteroatom in the polyaromatic core of the molecule.…”

Critical Review of Underlying Mechanisms of Interactions of Asphaltenes with Oil and Aqueous Phases in the Presence of Ions

“…The adsorption of asphaltenes at the interface is dependent on the interaction of functional groups and the other components in the oil phase (resin, aromatics, naphthenic acids) with the ions in the aqueous phase (salt). , Nordgard et al used polyaromatic surfactants with acidic groups to mimic surface-active agents’ behaviors. The film structure illustrated that these components form a stable interface due to acidic or possible hydrogen bonding with water molecules.…”

“…There is almost a common belief that asphaltenes are the same as surfactants. Asphaltenes containing heteroatoms act as surfactants and have a higher tendency to participate in the formation of the water–oil interface. ,, Despite that, the structure of not all the asphaltenes is the same as surfactants. Asphaltenes may contain polar, hydrophilic groups, while the alkyl chains of the asphaltenes are hydrophobic.…”