(308j) Using Microemulsion Phase Behavior As a Predictive Model for Lecithin-Tween 80 Marine Oil Dispersants

Marine oil dispersants are typically composed of a surfactant blend dissolved in solvents and, when introduced to the crude oil-seawater interface (OWI), they reduce the oil-water interfacial tension (IFT). This IFT reduction, coupled with wave action, facilitates the emulsification of the crude oil into the water column where it is eventually broken down by bacteria. Recently, questions about the environmental toxicity of commercial dispersant formulations have led to the development of new blends composed of the food grade surfactants L-α-phosphatidylcholine (lecithin) and polyoxyethylenated sorbitan monooleate (Tween 80). Individually, neither surfactant is effective at dispersing crude oil, but when combined at specific weight ratios, lecithin-Tween 80 (LT) blends work synergistically for effective dispersion. Moreover, it has also been observed that the effectiveness of these LT blends is not readily explained by the generalized properties thought to define surfactant potential for effective dispersants, and it is thought that other interfacial phenomena must have a role in effective oil dispersion. This work focuses on understanding the connection between LT ternary phase behavior (in dispersant-hexadecane-synthetic seawater systems; DHS) and dispersant effectiveness. Specifically, we hypothesize that the thermodynamic phase equilibria in DHS systems of a given LT dispersant blend correlates with that blend’s dispersant effectiveness. To test this, we have mapped microemulsion phase behavior (and how it changes with time) over the course of 8 weeks in DHS systems across 6 different lecithin:Tween 80 weight ratios: 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0. From this study, we have determined that there is an empirical correlation between LT dispersant effectiveness and the microemulsion phase behavior in these DHS ternary systems, and believe that the observed fundamental thermodynamic principles can be used as a predictive model and universal indicator of effective dispersant blends. Further, this presentation will outline a protocol that allows the phase behavior to be observed on industrially relevant timescales and discuss a set of general guidelines that can be used to interpret the results of these tests. These findings expand on the fundamental understanding of dispersant interfacial chemistry and provide a tool to guide the efficient formulation of future marine oil dispersants.