Asphaltene solvency and the role of asphaltenes and solids in emulsion stabilization

The goal of this investigation was to understand the mechanisms of petroleum emulsion stabilization. The study has focused on the role asphaltenes play in the formation of films at emulsion droplet interfaces, the primary mechanism by which water-in-petroleum emulsions are stabilized. The first part of this investigation dealt with the stabilization effectiveness of particles modified with adsorbed asphaltenes and resins. Stabilization effectiveness is dependent on the extent of asphaltene adsorption, controlled by solvency of asphaltenes. The second phase of this work was aimed at developing a fundamental understanding of the mechanism by which emulsions are stabilized. A new method of quantifying emulsion stability, the critical electric field (cef) technique, was utilized. Application of this method to heptane-toluene-asphaltene systems showed emulsion stability dependent on film thicknesses up to an interfacial asphaltene concentration corresponding to a monolayer of adsorbed aggregates. The interfacial concentration was proportional to the concentration of soluble asphaltenes. An investigation of cef with time was undertaken to develop a kinetic model for interfacial film formation. The model consisted of diffusion-limited asphaltene aggregate adsorption followed by consolidation of the adsorbed aggregates into an interfacial film. The model fit the data well and was used to determine asphaltene characteristics that control adsorption kinetics. Application of cef to petroleum systems enabled the construction of an emulsion stability correlation relating the product of asphaltene concentration and the difference in the H/C ratio of asphaltenes and the petroleum solvent to emulsion stability. In order to broaden the applicability of the correlation to petroleum blends, another correlating variable was introduced, the solubility parameter. Solubility parameters are volume additive, providing simple mixing rules. The third part of this investigation was the development of a routine to measure Hansen's three-dimensional solubility parameters of asphaltenes with refractive index measurements and solubility experiments. The measurement of solubility parameters was dependent on the state of asphaltene aggregation. Solvent systems that did not sufficiently disrupt aggregation were unable to probe the functionality of asphaltenes completely and could not be used to determine parameters. The use of appropriate solvent combinations produced parameters in agreement with previously published values.