Abstract:

Synthetic dispersants such as Corexit 9500A were used in large quantities (∼2 million gallons) to disperse the oil spilled in the ocean during the recent Deepwater Horizon event. These dispersant formulations contain a blend of surfactants in a base of organic solvent. Some concerns have been raised regarding the aquatic toxicity and environmental impact of these formulations. In an effort to create a safer dispersant, we have examined the ability of food-grade amphiphiles to disperse (emulsify) crude oil in seawater. Our studies show that an effective emulsifier is obtained by combining two such amphiphiles: lecithin (L), a phospholipid extracted from soybeans, and Tween 80 (T), a surfactant used in many food products including ice cream. Interestingly, we find that L/T blends show a synergistic effect, i.e., their combination is an effective emulsifier, but neither L or T is effective on its own. This synergy is maximized at a 60/40 weight ratio of L/T and is attributed to the following reasons: (i) L and T pack closely at the oil–water interface; (ii) L has a low tendency to desorb, which fortifies the interfacial film; and (iii) the large headgroup of T provides steric repulsions between the oil droplets and prevents their coalescence. A comparison of L/T with Corexit 9500A shows that the former leads to smaller oil droplets that remain stable to coalescence for a much longer time. The smaller size and stability of crude oil droplets are believed to be important to their dispersion and eventual microbial degradation in the ocean. Our findings suggest that L/T blends could potentially be a viable alternative for the dispersion of oil spills.

Suggested Citation:

Athas, Jasmin C., Jun, Kelly, McCafferty, Caitlyn, Owoseni, Olasehinde., John, Vijay T., and Raghavan, Srinivasa R.. 2015. An Effective Dispersant for Oil Spills Based on Food-Grade Amphiphiles. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N75B00DS

Publications:

Athas, J. C., Jun, K., McCafferty, C., Owoseni, O., John, V. T., & Raghavan, S. R. (2014). An Effective Dispersant for Oil Spills Based on Food-Grade Amphiphiles. Langmuir, 30(31), 9285–9294. doi:10.1021/la502312n

Purpose:

Our objective in this study was to identify dispersants that are safe, nontoxic, and environmentally benign while also having good dispersing ability against oil spills. Toward this end, we focused on food-grade amphiphiles that are commercially available. To identify effective dispersants, we studied the emulsification of one type of crude oil (a Louisiana crude obtained from the Macondo well in the Gulf of Mexico) against simulated seawater (i.e., water with added salts). Our studies revealed one promising candidate: a dispersant formed by blending lecithin and Tween 80. Lecithin is a phosphoplipid derived from soybeans that is commonly used as an emulsifier in the food industry, and it is also used to prepare liposomes for drug delivery. Tween 80 also called polysorbate 80, is a nonionic, single-tailed surfactant that is commonly used as an emulsifier in foods and pharmaceutical products.

Data Parameters and Units:

Figure S1. Synergistic emulsification of mineral oil by mixtures of lecithin (L) and Tween 80 (T). Mixtures of mineral oil and deionized (DI) water (3:7 ratio) are emulsified using either Lecithin alone, Tween 80 alone or a 60/40 mixture of Lecithin/Tween 80. Photographs are shown in each case for the sample immediately after preparation by vortex mixing, and 60 min after cessation of vortexing. Figure S2. Instability of O/W emulsions formed using Corexit 9500A. Crude oil and seawater (1:10 ratio) are emulsified using a 1:1 ratio of Corexit:oil (i.e., total concentration of dispersant is 10 wt%). Photographs are shown for the sample immediately after preparation by vortex mixing, and 30 min after cessation of vortexing. Figure S3. Emulsification using 60/40 L/T: Studies at different oil:water ratios. Figure S4. Emulsification using 60/40 L/T: Studies at different dispersant:oil ratios. The results discussed in the main manuscript are for samples at a crude oil:seawater ratio of 1:10 (Figure 4). Here the oil:water ratio is reduced to 1:15 and 1:25. Micrographs and photographs are shown for the sample immediately after preparation by vortex mixing, and 30 min after cessation of vortexing. The mean droplet diameter was obtained by image analysis using ImageJ. Figure S5. Emulsification using different surfactant mixtures with the same HLB (10.8). The crude oil:seawater ratio for these experiments is 1:10 and the dispersant:oil ratio is 1:1 (i.e., the total surfactant in each sample is 5 wt%). Photographs are shown for the sample immediately after preparation by vortex mixing, and 30 min after cessation of vortexing.

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