Effect of sodium citrate on asphaltene film at the oil-water interface

Sodium citrate (Na₃Cit) has been proven to improve the oil sands extraction recovery, but its mechanism is still unclear. Here we hypothesize that the presence of Na₃Cit affects the asphaltene behaviour at the oil-water interface, which enhances oil-water separation and, thereby, heavy oil recovery.

Na₃Cit-asphaltene interaction was first investigated on their interfacial shear rheology at one heptol-water interface. Na₃Cit-asphaltene interaction was further revealed by measuring the interaction forces between two heptol-water interfaces using the atomic force microscopy droplet technique combined with the Stokes-Reynolds-Young-Laplace (SRYL) model. Interfacial properties were further illustrated through interfacial tension, zeta potential, Langmuir trough, and FE-SEM.

Na₃Cit was found to weaken the strength of the asphaltene film at the heptol-water interface. Moreover, Na₃Cit could diminish the adhesion forces observed between two asphaltene-in-heptol droplets in high salinity solutions. Besides, Na₃Cit also made the asphaltene-in-heptol droplet more negatively charged. These results collectively suggest that Na₃Cit-asphaltene interaction results in a looser and more elastic asphaltene interfacial network with the slow formation and reduces the adhesion between two interfaces, all of which are most likely the consequence of increased electrostatic repulsion between asphaltene interfacial nanoaggregates. Our study provided new understandings of Na₃Cit-asphaltene interactions at the interface.