Asphaltene : big molecules causing big problems

Asphaltenes are complex polar components of heavy oils and are only marginally stable in organic solvents. Because of this marginal solubility, they have a propensity to adsorb onto oil/water interfaces to form viscoelastic layers. This can result in a strong stabilization of water- in-oil emulsions that cause difficulties in refining operations. In this work we examine the coalescence process of both water and oil droplets against an oil/water interface in the presence of asphaltenes using a newly developed instrument where the thickness of thin, draining films can be measured in space and time. Using this instrument, thin film thickness, internal droplet pressure and coalescence times can be measured. In addition to asphaltene concentration in a model hydrocarbon (toluene is used), the aging times of the interface was varied. Both asphaltene concentration and aging time are found to strongly affect the coalescence dynamics for the water droplet. On the contrary, for the oil droplet the coalescence dynamic was independent of either concentration or aging time. In addition to reporting on droplets coalescence dynamics, we found that contact of water against asphaltene/toluene solutions induced the production of a remarkable spontaneous emulsification where micron-sized water droplets, stabilized by asphaltenes, spontaneously appeared.