Molecular dynamics simulation of demulsification of O/W emulsion containing soil in direct current electric field

• NPs plays different roles in different stages of demulsification. • SDS molecules will hinder the fusion of oil droplets in low electric field. • The formation of bridge structure is the key of oil droplet demulsification. • The fusion process of oil droplets can be divided into four stages. The collision under direct current (DC) electric field and non-electric field coalescence behavior of heavy oil droplets in complex oil-in-water (O/W) emulsion system were studied by molecular dynamics (MD). By changing the simulation parameters of electric field intensity, the movement of various molecules of emulsified oil droplets, such as Sodium dodecyl sulfate (SDS) molecules, silica nanoparticles (SiO 2 NPs), asphaltene and resin molecules under six electric field intensities, and the aggregation process of colliding oil droplets after electric field excitation are discussed. At the same time, the radial distribution function and conformational statistics are used to analyze the charge distribution of oil droplets and the change of interaction force of different molecules from the microscopic point of view, and further explore the demulsification mechanism of oil droplets under the electric field. The simulation results show that when the electric field intensity is lower than 1.5 V/nm, the oily components of emulsified oil droplets cannot contact because of the blocking effect of SDS molecules. When the electric field intensity is greater than or equal to 1.5 V/nm, SDS molecules separate from the oil phase and enter the water phase, and emulsified oil droplets contact. The interface is a bridge structure formed by the face-to-face accumulation of asphaltene and resin. The existence of this structure is the key to further coalesce oil droplets into a whole. The local oil droplets will spontaneously coalesce without electric field, and the bridge structure formed by asphaltene will gradually disappear. SiO 2 nanoparticles will promote the coalescence of oil droplets.