Dispersants used in the mitigation of oil spills are mixtures of amphiphilic molecules in a solvent. The recent large-scale use of dispersants has raised environmental concerns regarding the safety of these materials. In response to these concerns, we have developed a class of eco-friendly dispersants that utilize food-grade amphiphiles such as the phospholipid lecithin (L) (from soy) and the nonionic surfactant Tween-80 (T) to effectively disperse crude oil into seawater. This combination of surfactants stabilizes the oil-water interface, forming stable emulsions. Stabilization is maximized at a 60:40 weight ratio of L/T, whereas stable emulsions are not observed for either L or T individually. This talk will discuss reasons for the above synergistic response. Relevant factors include: (i) close packing of L and T at the interface, (ii) low tendency of L to desorb from an LT interface and (iii) steric stabilization of droplets provided by the large oxyethylene head groups of T. The second aspect of this talk will focus on the solvent used in LT dispersants. The initial solvent was ethanol, which is relatively nontoxic but is also quite volatile (low flash point). Typically, solvent choice has been based on factors like the volatility or viscosity of the overall mixture; however, solvents are considered to have minimal effect on dispersion efficiency. Here, we show that the solvent can have a dramatic impact on dispersion efficiency, i.e., on the extent to which a thin layer of oil is dispersed in the water column for a given amount of LT dispersant. For example, with the same surfactants, the dispersion efficiency can range from &gt; 75% in one solvent to &lt; 10% in another. We have attempted to devise a systematic procedure to select the optimal solvent. In this regard, we turned to Hansen Solubility Parameters (HSPs), which are 3-D representations of solvent properties. We assessed the quality of dispersion for a large range of solvents through a low-energy dispersion test and plotted the results on the above 3-D plot. A systematic trend is seen, with optimal solvents clustering around a particular region of the plot. Through this analysis, we will identify solvents that combine high dispersion efficiency, good solubility of the LT amphiphiles, and also have a low toxicity profile.

Food-grade dispersants for remediation of oil spills: Insights from colloid science

254th National Meeting (2017)

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