Water-in-hydrocarbon emulsions stabilized by asphaltenes at low concentrations

The role of Athabasca asphaltene particles and molecules in stabilizing emu lsions was examined by measuring the surface area of water-in-toluene/hexan e emulsions stabilized by various asphaltene fractions, each with a differe nt proportion of soluble and insoluble asphaltenes. The stabilized interfac ial area was found to depend only on the amount of soluble asphaltenes. Fur thermore, the amount of asphaltenes on the interface was consistent with mo lecular monolayer coverage. Hence, at low concentrations, asphaltenes appea r to both act as a molecular surfactant and stabilize emulsions. The effect of the hexane : toluene ratio on emulsion stability was examined as well. At lower hexane:toluene ratios, more asphaltenes were soluble but the surfa ce activity of a given asphaltene molecule was reduced. The two effects opp ose each other but, in general, a smaller fraction of asphaltenes appeared to stabilize emulsions at lower hexane:toluene ratios. The results imply th at the emulsifying Capacity of asphaltenes is reduced but not eliminated in better solvents. (C) 2000 Academic Press.