Effect of Dispersant on Asphaltene Suspension Dynamics: Aggregation and Sedimentation
Sara M. Hashmi and Abbas Firoozabadi
When oil is mixed with light alkanes, asphaltenes can precipitate out of oil solutions in a multistep process that involves the formation of nano and colloidal scale particles, the aggregation of asphaltene colloids, and their eventual sedimentation. Amphiphilic dispersants can greatly affect this process. The mechanism of the dispersant action in colloidal asphaltene suspensions in heptane has been shown through previous work to be due in part to a reduction in the size of the colloidal asphaltene particles with the addition of dispersant. However, previous studies of the sedimentation behavior revealed evidence of aggregation processes in the colloidal asphaltenes in heptane that has yet to be investigated fully. We investigate the effect of dispersants on this aggregation behavior through the use of dynamic light scattering, showing that both the amount of dispersant and the amount of heptane dilution can slow the onset of aggregation in colloidal asphaltene suspensions. An effective dispersant acts by suppressing colloidal aggregation in asphaltene suspensions, as shown by light scattering, and therefore also slows separation from the bulk, as revealed through macroscopic sedimentation experiments.
Sara Hashmi, Director of the Facility for Light Scattering, devoted much of her postdoctoral research to understanding and controlling the precipitation of asphaltenes from petroleum fluids. Read on for additional and subsequent work that highlights the importance of electrostatic interactions in these unique non-polar dispersions:
Acid-base chemistry enables reversible colloid-to-solution transition of asphaltenes in non-polar systems, by Hashmi, Zhong, and Firoozabadi. Soft Matter 8, 8778 (2012).
Polymeric Dispersants Delay Sedimentation in Colloidal Asphaltene Suspensions, by Hashmi, Quintiliano, and Firoozabadi. Langmuir 26, 8021 (2010).