Enhanced separation of oil-in-water emulsion by cyclic penetration of emulsion droplets through an oil layer

Abstract

The separation of emulsion components is a typical heterogeneous phase separation process. This process can be promoted by coalescence of the dispersed phase droplets. However, the coalescence would be inhibited due to the interface between the continuous and dispersed phases. The separation efficiency can be increased by increasing the probability of collisions between the droplets, and this can be realized by increasing the area of contact among the dispersed phase droplets. In this study, a new enhanced separation method involving the circulation of emulsion droplets containing an emulsified oil phase through an oil layer is proposed. The migration of the emulsified oil phase from the millimeter-sized droplets to the oil layer was studied. This migration enabled efficient separation of the oil and water phases, and this process was assessed by using a dyeing agent in the oil phase and by monitoring the variation in the turbidity. The influence of main factors such as the circulating droplet size, thickness of the oil layer, and effect of the circulation rate on the separation was determined. The turbidity of the emulsion reduced from 394.33 NTU to 10.98 NTU, with a separation efficiency of 97.22 % under the optimum operation conditions. The linear fitting relationship for the main factors that affect separation with the duration or number of circulation cycles was obtained. The results indicate that the novel strategy of using an additional oil layer and circulating emulsion droplets through it is promising for oil–water separation, especially via gravity separation.