Date of Award

8-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Earth Science

Advisor

Ladner, David A

Committee Member

Karanfil , Tanju

Committee Member

Freedman , David L

Committee Member

Ladner , David A

Abstract

Dendritic polymers have recently been shown to entrap polycyclic aromatic hydrocarbons (PAHs) and other hydrophobic materials. Laboratory results have shown that poly(amidoamine) dendrimers and hyperbranched poly(ethyleneimine) polymers form complexes with linear (hexadecane) and polyaromatic (phenanthrene) hydrocarbons, increasing the dispersion of these model crude oil components. It is thus hypothesized that crude oil can be dispersed using these polymers. Compared with commercial dispersants, dendritic polymers have the potential to be more biocompatible and less toxic. The objective of this research was to gain a fundamental understanding of the interactions of dendritic polymers with crude oil. We used Louisians Sweet Crude oil to explore the dispersion effectiveness of the polymers and the mechanisms of oil-polymer interactions. Results were compared with Corexit 9500, the dispersant used in response to the Deepwater Horizon disaster of 2010. We investigated the factors that may influence the experimental results, such as dispersant to oil ratio (DOR), mixing and settling time, sample preparation methods and sample collection methods to establish experimental protocols that adequately characterized the effectiveness of the polymers. The effects of polymer size and surface groups on oil dispersion effectiveness were examined through an optimized effectiveness test. Five hyperbranched polyethylenimine polymers (HY-PEI) with molecular weight 1.2, 1.8, 10, 70 and 750 kDa and amino surface terminal groups were examined with the effectiveness test. The results showed the 10 kDa HY-PEI had the highest dispersion efficiency (58%) slightly larger than Corexit (56%). 70 kDa and 750 kDa HY-PEI also had a relatively high effectiveness, 48% and 40% respectively; however, the low molecular weight polymers, 1.2 kDa and 1.8 kDa had low dispersion efficiency, 11% and 17%, similar to the no dispersant scenario which had 13% oil dispersion. We also tested three dendrimers with different surface terminal groups: amino (positive charge), amidoethanol (neutral charge) and succinamic acid (negative charge). The results showed that G4-PAMAM-NH2 with positive surface charge had the highest efficiency of these three, 42%. G4-PAMAM-OH and G4-PAMAM-SA had lower dispersion capacity, with effectiveness of 16% and 19%. We concluded that the polymers with moderate size and positive charged surface groups are very capable in dispersing light sweet crude oil. Further exploring the interactions of dendritic polymers with crude oil, we conducted dynamic interfacial tension test and oil droplet size distribution test. The dynamic interfacial tension curves shows that all the polymers can reduce the interfacial tension and the larger polymers are more capable at decreasing the interfacial tension rapidly. The efficiency of polymer dispersion for oil has also been verified by drop size distribution measurements. Polymers with high performance in effectiveness test tend to create smaller droplets than polymers that show less effectiveness. Again, moderately sized polymers gave the smaller average droplet size and polydispersity. By further analyzing the data we developed a conceptual model for the oil dendritic polymer interaction, which is a hybrid surfactant and Pickering emulsion mechanism.

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