Deformation and breakup mechanism of water droplet in acidic crude oil emulsion under uniform electric field: A molecular dynamics study

Abstract

If the critical field strength (Ec) is exceeded, the droplets in water-in-oil (W/O) emulsions would undergo severe electrodispersion during the electric dehydration. Naphthenic acid (NA) is an essential constituent of acidic crude oil. To reveal the mechanisms behind the deformation and breakup of water droplets in acid-containing emulsions, a molecular dynamics method was employed to investigate the motor behavior of a single water droplet at different field strengths. Weak interaction analysis indicated that naphthenic acid formed a strong hydrogen bond (H-bond) with water, and a low-intensity dispersion attraction with n-hexane. The carboxyl group on NA was mainly adsorbed on the surface of droplet via electrostatic interaction, and the H-bond between the two has a lifetime of 2.14 ps at 0.6 V nm−1 field strength (E). Despite the presence of NA, H2O and ions are crucial factors influencing droplet deformation and breakup, respectively. The radius of gyration may allow for quantitatively evaluating the degree of droplet breakup. Potential energy analysis showed that the Coulomb interaction between NA molecules significantly affected their migration in the system. The dipole moment of NA driven by external electric field is parallel to the field direction. Our studies provide a molecular-level framework for understanding the movement of water droplets in acid-containing oil under applied electric field.