Mechanisms on the stability and instability of water-in-oil emulsion stabilized by interfacially active asphaltenes: Role of hydrogen bonding reconstructing

Abstract

Chemical demulsification is the most commonly used demulsification method for the separation of oil–water emulsions (W/O) in petroleum industry. Previous experiments demonstrate that the interfacially active asphaltenes (IAA) play the key role in stabilizing the heavy oil–water emulsions. Herein, the molecular dynamic simulation has been applied to reveal the molecular mechanisms on the stability and instability of the IAA-stabilized oil–water emulsions. It is found that IAA could accumulate at the oil–water interface and self-aggregate to form viscoelastic interfacial film through π-π stacking, hydrogen bonds (intermolecular and intramolecular) and other non-covalent bonds. Different types of hydrogen bonds (i.e., S = O…H-O, R-OH…H-O, N-H…N-R, S-H…S = O, S-H…S-R) are found between the IAA molecules due to the presence of heteroatoms (e.g., N, O, S) in IAA. Increasing the IAA concentration would increase the thickness of the IAA film which plays the key roles in stabilizing the emulsions. When the newly synthesized demulsifier (i.e., MJTJU-2) was added into the oil–water emulsion system, the oxygen groups (i.e., hydroxyl, ester groups, carboxyl groups, ether group) in demulsifier could weaken (at least 50%) or even break the hydrogen bonds and π-π stacking between IAAs and form new stronger hydrogen bonds with water molecules. This hydrogen bond reconstruction facilitates the breaking of the IAA film at the oil–water interface, allowing the coalescence of the water droplets in oil phase. This work would provide fundamental understanding for developing new way to efficiently demulsify the petroleum or similar oil–water emulsions.