274327 Electrostatics in Non-Polar Systems: Transitions From Unstable Colloids to Molecular Dissolution Via Polymeric Functionalization
Asphaltenes, the most aromatic and largest molecular weight component of petroleum fluids, tend to phase separate under a variety of conditions, causing many problems for hydrocarbon energy production in the petroleum industry. While large amounts of aromatic solvents provide a thermodynamic mechanism for addressing asphaltene precipitation, their use is neither economical nor environmentally friendly. Methods requiring smaller doses of chemicals are highly preferred. However, chemical design principles for asphaltene dispersants require detailed understanding not only of asphaltene chemistry on the molecular scale, but also of the interactions governing asphaltene dynamics on colloidal length scales. One additional challenge for asphaltene stabilization lies in the non-polar nature of petroleum itself. Electrostatic interactions, ubiquitous for stabilizing aqueous suspensions, provide a double-edged sword in non-polar media: they are both strong and long-range. While mixtures of homogeneously charged molecules or particles will remain stable, even small amounts of heterogeneous surface charging can lead to destabilization and separation.
During my postdoctoral research, I seek to understand the fundamentals of asphaltene stabilization by dispersants by using a variety of experimental methods, including static and dynamic light scattering, UV-visible spectroscopy, and measurements of bulk conductivity and sedimentation dynamics. Both non-ionic and ionic dispersants can stabilize asphaltenes at different stages in the precipitation process, albeit through very different mechanisms: the first involving polymeric adsorption onto colloidal surfaces and the second relying on acid-base interactions at the molecular level. My work has uncovered several unique aspects of asphaltenes from a materials science perspective, including the presence of both positive and negative surface charges on unstable asphaltene colloids and the importance of heteroatomic content in tuning the solubility characteristics of these π-conjugated materials. Furthermore, the different mechanisms of action of the non-ionic and ionic dispersants at the molecular and colloidal scales have consequences for their utility in addressing the main industrial concern: asphaltene precipitation in wellbores and pipelines. I will also describe measurements assessing dispersant effectiveness for both inhibiting and reversing asphaltene deposition from bulk flows.