Asphaltene Self-Assembly

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Title: Asphaltene Self-Assembly
Author: Verruto, Vincent J.
Advisors: Peter K. Kipatrick, Committee Chair
Jan Genzer, Committee Member
Orlin D. Velev, Committee Member
Saad A. Khan, Committee Member
Abstract: Despite a strong push for alternative energy, fossil fuels remain an important energy source given an ever-increasing global energy demand. As crude oil prices continue to soar, petroleum producers and refiners are looking to “unconventional†crudes, such as bitumen and heavy crude oils, to meet their needs. Unlike light-sweet “conventional†feedstocks, heavy crudes are often rich in a fraction that is characteristically polydisperse, of high-MW, polyaromatic, polar, and surface-active. Consequently, asphaltenes present expensive challenges associated with aggregation, flocculation, precipitation, deposition, and emulsion stabilization. The scope of the work here focuses on two important aspects of asphaltene self-assembly: bulk phase aggregation and interfacial film formation. Using small-angle neutron scattering (SANS) we expand the description of these aggregates beyond their size (~50-100 Å), shape (discoidal), and degree of solvent entrainment (30-50% by volume), to also include the entrained solvent composition when dissolved in binary solvent mixtures. We then use SANS to evaluate the physical and chemical properties of the stabilizing interfacial films in water-in-model oil emulsions. In Part I of this SANS of emulsions investigation, we unravel the thickness and asphaltenic composition of the interfacial films from emulsions made in three solvents of varying aromaticity. We will show that for these three systems, emulsion stability depended on the asphaltenic composition in the films as opposed to the film thickness, which was nearly constant among the three solvents. In the Part II we seek a more thorough definition of the interfacial film composition by using neutron contrast variation to illuminate not just the asphaltenic makeup, but the solvent, water, and, when applicable, additive composition within the films. Finally, through the use of interfacial shear and dilatational rheology, we explore the various interactions at model oil/water interfaces that influence interfacial film assembly. We find that electrostatic interactions between charged adsorbed species largely dictate the transient evolution of the interfacial elasticity at acidic, neutral, and basic pH. Furthermore, through our comparisons of the interfacial rheological behavior of asphaltenes and model polycyclic compounds, we are able to better understand the physicochemical phenomena that contribute to asphaltene interfacial dynamics.
Date: 2008-11-07
Degree: PhD
Discipline: Chemical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/2989


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