(93g) Efficient Dispersion of Crude Oil By Blends of Food-Grade Surfactants: Toward Greener Oil Spill Treatments
Recent work has suggested that marine oil dispersants containing blends of the nontoxic surfactants lecithin (L) and Tween 80 (T) may be effective alternatives to traditional dispersant formulations containing blends of Tween 80, Span 80, and DOSS (dioctyl sodium sulfosuccinate). The dispersion effectiveness of lecithin-Tween 80 (L-T) blends in an ethanol solvent was measured for South Louisiana crude oil using baffled flask effectiveness testing, as a function of L:T ratio, surfactant:solvent ratio, solvent composition, and wt% dispersant in oil. The most effective L-T dispersants performed comparably to Tween 80-Span 80-DOSS dispersants, dispersing 75-90% of the test slick at 1.25-5 wt% dispersant in crude oil. Increasing surfactant:solvent ratio increased dispersant effectiveness even when dispersant dosage was proportionally reduced to keep total wt% surfactant in the oil constant. Replacing some of the ethanol solvent with octane or octanol also increased dispersant effectiveness, suggesting that ethanol's hydrophilicity lowered dispersant-oil miscibility, and that more hydrophobic solvents would increase dispersant effectiveness.
Two other important findings were that:
(1) lecithin-rich L-T dispersants were significantly more effective than Tween 80-rich L-T dispersants with lower or comparable interfacial tension, and
(2) all L-T dispersants produced much higher interfacial tension than Tween 80/Span 80/DOSS dispersants.
This suggests that interfacial phenomena other than interfacial tension, such as the formation of an interfacial gel or oil-dropletsâ resistance to coalescence, may also influence L-T dispersantsâ effectiveness.