Breaking of Emulsions with Chemical Additives: Using Surrogate Fluids to Develop a Novel Theoretical Framework and Its Application to Water-in-Crude Oil Emulsions

We investigate the role of adding a water-soluble surfactant (Tween 20) that acts as a demulsilier on the stability of water-in-dodecane emulsions stabilized with Span 80. Performing bottle test experiments, we monitor the emulsion separation process. Initially, water droplets sediment fast (similar to 10 min) until they become closely packed and form the so-called dense packed layer (DPL). The presence of the DPL, a long-lived metastable high-water-fraction (70-90%) emulsion separating bulk oil and water layers, slows down significantly the kinetics (similar to 10(5) min) of water separation. Once the DPL is formed, the ratio of the volume of separated water to the total water amount is called as water separation efficiency. We assume that the emulsion stability is reached when the coverage of the emulsifier surfactant exceeds 80% and use the ideal solution approximation. From that, we rationalize the water separation efficiency and the minimum demulsifier concentration required to maximize it, in terms of the mean droplet size, the surfactant concentrations, the total water volume fraction, and the adsorption strength of the water-soluble surfactant. Model predictions and experimental findings are in excellent agreement. We further test the validity and robustness of our theoretical model, by applying it successfully to data found in the literature on water-in-crude oil emulsion systems. Ultimately, our results prove that the efficiency of a demulsifier agent to break a W/O emulsion strongly correlates to its adsorption strength at the W/O interface, providing a novel contribution to the selection guidelines of chemical demulsifiers.

Automated summary

The study investigates the role of adding a water-soluble surfactant as a demulsifier in stabilizing water-in-dodecane emulsions. The formation of a dense packed layer significantly slows down water separation, leading to an increased water separation efficiency. The efficiency of demulsifiers in breaking W/O emulsions is strongly correlated to their adsorption strength at the W/O interface, providing valuable insights for chemical demulsifier selection.