Droplet behaviors of W/O emulsions under the combination of electric field and medium coalescence

The efficient separation of water-in-oil emulsions plays an important role in many industrial fields. However, the demulsification performance using a single method is limited. In recent years, a novel deep purification method combining direct current electric field and medium coalescence has been proposed. To better understand the mechanism of this process, this work investigated the behavior of water droplets at different conditions. The results show that all injected water droplets initially migrate toward the charging side, while the opposite movement of some droplets is due to collision with the others or breakage from the original ones. The droplets migrated back and forth between electrodes through the polarize-discharge process. However, owing to the heterogeneous electric field near the charging side, some large-size droplets rebounded at a certain distance away from the charging electrode, leading to a counterflow of W/O emulsion during electrostatic coalescence. Moreover, the higher voltage leads to the faster coalescence of dispersed droplets on the medium surface, and the wetted medium can redistribute the electric field. With the collision and the deposition of water droplets, different kinds of water areas were formed and kept a dynamic equilibrium on the medium surface. The subsequent water droplets deposited on the medium surface and then flowing away along these areas. The results proposed in this paper present an in-depth understanding of the mechanism of the electrocoalescence, the medium coalescence, and the combination of them, which provides useful insights for the design of demulsification device and the separation process of W/O emulsion.