Electric double layer effects in water separation from water-in-oil emulsions

Abstract

Abstract Separating water from water-in-oil emulsions is crucial for upgrading of crude oil, water harvesting, etc. In this paper, we develop a theory to propose a new mechanism of separating water from water-in-oil emulsions by utilizing the electric double layer (EDL) effects induced by introducing a separator that is either a charged or an ionizable surface (e.g., a glass) inside this emulsion. This surface gives rise to an EDL inside those water droplets that settle on it due to wettability differences. The EDL triggers a hydrophilicity-inducing tendency, since the resulting EDL electrostatic wetting tension enforces a “electrowetting”-like behaviour of the water droplets. We develop a free-energy-based calculation to establish that such EDL-induced “electrowetting” behaviour enforces a much more spontaneous water separation from the emulsion. Our analysis further establishes that the dependence of this degree of spontaneity of separation on the salt content and the pH of the water drop.