Date of Award

8-2016

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Earth Science

Committee Member

Dr. David Ladner, Committee Chair

Committee Member

Dr. Kevin Finneran

Committee Member

Dr. David Freedman

Abstract

The Deepwater Horizon oil spill in 2010 marked one of the biggest spills in history. Like many other oil spills, Corexit 9500 was used to attempt to prevent some of the environmental impacts of the spill. The abundant use of Corexit during this spill raised public awareness and called into question the dispersant’s toxicity and long-term impacts on the environment. These concerns brought to light the need to discover less toxic, more biodegradable oil dispersants. This research helps determine the feasibility of using hyperbranched polymers (HBP) as oil dispersants by comparing their oil dispersion effectiveness to that of the commonly used dispersant, Corexit 9500. Hyperbranched polyethylenimine (Hy-PEI) polymers of various molecular weights were the first potential dispersants tested. In artificial seawater with a 0.02 (1:50) dispersant-to-oil ratio (DOR) Hy-PEI polymers with low molecular weights (1.2 and 1.8 kiloDaltons [kDa]) showed very little dispersion capability. The higher molecular weights (10, 70, and 750 kDa) showed better dispersion potential; however, only 10 kDa had an oil dispersion efficiency (82.9%) as high as Corexit (72.9%). The effectiveness of the Hy-PEI polymers and Corexit was also determined for a range of DOR’s. For each polymer and Corexit the DOR was varied from .0015 to 1. The goal was to observe how increasing the amount of dispersant applied to the oil affected how well the oil was dispersed. With increasing DOR , 1.2 and 1.8 kDa had a slight increase in dispersion effectiveness. Both Corexit and 10 kDa showed an increase in dispersion effectiveness as DOR increased. However, 70 and 750 kDa appeared to have a maximum dispersion effectiveness at a 0.02 DOR, followed by a decrease in effectiveness as their DOR was increased. It is likely that as the DOR of the larger polymers were increased passed 0.02, they began to interact more with each other and resulted in an agglomeration of dispersant that decreased their ability to keep the small oil droplets dispersed. The effectiveness of the Hy-PEI polymers and Corexit was also determined for various aquatic environments. In order to stimulate different environments that could be exposed to oil spills, the salinity and pH of the artificial seawater used in the dispersion tests was altered. Artificial seawater was diluted with DI water in order to achieve saltwater with 0, 10, and 35% of the original seawater salt concentration. The clearest trends were seen with Corexit, 70 kDa, and 750 kDa. Corexit showed an increase in effectiveness as salt concentration increased. This is due to Corexit being designed with surfactants that are tailored to higher salinities. In freshwater, the surfactants in Corexit are altered to promote water-in-oil emulsions, this prevents the surfactants from adequately stabilizing the oil droplets in the water column. However, with the 70 and 750 kDa Hy-PEI polymers, there appeared to be a drop in dispersion effectiveness at the highest salinities. It is possible that high ionic strength increased the aggregation of the polymers with high molecular weights. In addition to the Hy-PEI polymers, various HBP’s with a polyethylene glycol core and polyester links (Hy-PE-PEG polymers) were also tested for dispersion capabilities. These were chosen because their hyperbranched structure is made up of polyester linkages. Polyester linkages have been shown to have higher biodegradability than PEI, making the Hy-PE-PEG polymers potentially more appropriate for environmental remediation. Also, their neutral end groups are less toxic to aquatic organisms than the positively charged end group of the Hy-PEI polymers. However, the lack of positively charged end groups also appeared to decrease dispersion effectiveness; none of the Hy-PE-PEG polymers demonstrated a dispersion effectiveness as high as that of Corexit.

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