Acknowledgements

None of this work would have been possible without the help of those around me. I would like to thank Dr. Corbett and Dr. Freedman for use of their lab space and for advising me on this project. Both of my parents have supervised me supported me through the roller coaster that science often is. My mom taught me how to make plans and use a calendar, and my dad helped me run experiments. I'd especially like to thank my grandmother, Kathy, for sparking my interest in science and teaching me to be an environmentalist from the beginning. I've solved many of the problems I've encountered by talking with her. I am incredibly grateful to be surrounded by people who are

Background

Despite the frequency of oil spills decreasing dramatically over the past 30 years, oil spills remain a large problem. (ITOPF, 2021) In the 2010s, oil tankers alone released 164,000 tonnes of oil.(ITOPF, 2021) These spills negatively impact human health, ecosystems, tourism, and local economies.(Gulf Coast Ecosystem Restoration Council, 2020) The current methods for removing oil from the environment rely heavily on oil dispersants, a specialized type of surfactant. Notably, oil dispersants were used on a very large scale (>1.8 million gallons) to address the Deepwater Horizon (DWH) oil spill.(McCenity, 2014) The use of oil dispersants aims to form small droplets of oils, called micelles, which are then dispersed throughout the water column by wave action. Generally, oil dispersants are applied in an attempt to prevent an oil slick from reaching shore, both for environmental and public relations reasons.(D’Ambrose, 2016). When the droplets of oil are dispersed throughout the water column, the overall area of the water-oil interface increases. Oil consuming microorganisms can only consume oil from this interface, therefore the application of oil dispersants tends to increase the biodegradation rate of oil.(D’Ambrose, 2016; McCenity, 2014)

While oil dispersants certainly decrease the visual impact of oil and increase the degradation rate, their benefits must be weighed against the cost of releasing potentially toxic compounds into the environment. In the DWH spill, very large amounts of Nalco’s Corexits 9527 and 9500 were used to treat the spill.(National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, n.d.) In laboratory tests, exposure to either product resulted in harm to crustaceans, fish, and corals at concentrations less than 20ppm and almost universally resulted in death at concentrations above 100ppm.(Wise & Wise, 2011) To neglect the advantages of oil dispersants would be foolish, however, less harmful alternatives to the existing options must be developed before dispersants can be used without causing more harm than good.

Surfactants are effective at forming stable droplets of oil because they are amphiphilic, with a hydrophilic (polar) head group and a lipophilic (nonpolar) tail. (National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, n.d.) Surfactants stabilize the oil-water interface because the molecule spans the interface, with the tail attracted to oil and the head attracted to water. (Davies, 1957) When surfactant is applied to a mixture of oil and water, the mixture changes from an oil layer and a water layer to a single layer consisting of small droplets of one layer evenly dispersed throughout the other. Whether a given surfactant produces droplets of oil in water or droplets of water in oil depends on its hydrophilic-lipophilic balance (HLB), as defined below.(Davies, 1957)

HLB= ∑H+n(-0.475)

H = HLB group number of hydrophilic groups on head

n = number of CH¬2 groups in tail

Values for HLB group numbers can be found in Davies’ original paper

The goal of oil dispersants is to dissolve a comparatively small amount of oil into a large volume of water. According to Davies, surfactants are able to solubilize oil in water only when their HLBs are greater than 15.

Beeswax has great potential for use as the hydrophobic tail of surfactants. It is primarily composed of fatty alcohols and acids, with a chain length of C20 to C36. These constituents, along with their esters, comprise about 75% of beeswax by mass, with an additional 15% of C23 to C35 of straight chain alkanes. The remaining 10% are trace compounds that provide beeswax it’s unique color and scent. (Svecnjak et al., 2019) By hydrogenation, the fatty acids may be reduced to alkyl-1-ols, commonly used building blocks for surfactants.(Whyte, 1955)

Designing an Effective Oil Dispersant

The four main factors that were considered when designing oil dispersants were HLB, toxicity, solubility and biodegradability. HLB was above 15 for all dispersant structures considered, but otherwise was not a major consideration. For both the workers and the environment exposed, minimizing toxicity was a major concern. To avoid toxicity, structures containing covalently bonded halogens and ether groups were not considered .(Ruder, 2006; US Department of Health and Human Services, 1998, pp. 151–184) Using beeswax as a feedstock reduces toxicity because of its long chains, high molecular weight compounds are less able to penetrate cell membranes.(Bos & Meinardi, 2000) Most oil dispersants are used in seawater; therefore, the common-ion effect must be considered to prevent oil dispersants from precipitating. The most common ions in seawater are Na+ and Cl-, these ions were substituted for K+ and Br- in all dispersants considered.(US Environmental Protection Agency, n.d.) Biodegradability is a difficult balance to strike, if the dispersant is too biodegradable, it will biodegrade before bacteria can degrade oil, however, if it is insufficiently biodegradable, the dispersant will become a persistent organic pollutant. Considering all of the variables above, two surfactants were selected for synthesis, potassium alkyl sulfate and alkyl glycoside.

Potassium alkyl sulfate (PAS) consists of an alkane chain with a potassium sulfate salt on one end. Little research has been done on PAS; however, it is chemically similar to sodium dodecyl sulfate (SDS), differing only in cation and carbon chain length. SDS has a very large body of research on it because it is commonly used in household products. SDS is highly biodegradable, with a half life of 48h at 10C, (Margesin & Schinner, 1998) In addition, SDS is nontoxic, aside from a risk of skin irritation at high concentration, and poses no long term exposure hazards. (Blondi et al., 2015). Based on these properties of SDS, PAS meets many of the requirements of a good oil dispersant.

The Alkyl Glycoside (AG) synthesized in this project is alkyl ß-D-glucopyranose, consisting of a D-glucose bound with an ester bond at the 2 position to an alkane chain. Such a bond can form because the hydroxyl group at the 2 position is acidic, due to the nearby electronegative oxygen. Alkyl glucosides are widely used in biology laboratories as a nonionic detergent. (ThermoFisher Scientific, n.d.) AG is also comparatively biodegradable, with a half-life between 5 and 10 days. Alkyl glycosides are naturally occurring biomolecules, particularly in plants(van Rantwijk et al., 1999). AGs are considered safe, but there is some evidence of them causing dermatitis in susceptible humans. (Loranger et al., 2017)

SERMACS Poster

When I presented the poster, I was planning to run a synthesis on Quaternary Ammonium Bromide salts, but I have chosen to stop pursuing that route due to toxicity and time concerns

Methods

I've developed several methods to purify fatty alcohols and to add polar headgroups. Two of the procedures I am most proud of are below: