Coalescence of oil microdrops in the flow of emulsions past solid surfaces

Abstract

Oil-in-water emulsions at concentrations of 0.001‐ 1 vol % are very important objects because they are involved in fine water treatment to remove oil microdrops and in the formation of cruds, which cause a nuclear hazard in radiochemical extraction processes. In this work, a method was proposed for studying the coalescence of microdrops of organic liquids on the surface of solids and cloths. It was shown that the determining step is a second-order process occurring on the collision of microdrops coming from the bulk with drops of surface clusters. Once the microdrop size has become smaller than a certain value, the process rate constant significantly decreases. It was found that the decisive role in the microdrop coalescence is played by the pH of the oil-in-water emulsion and the specific surface area of solids. The proposed mechanism accelerates the separation of oil drops from water by a factor of hundreds or thousands.