Energy & Fuels, Vol.30, No.7, 5240-5252, 2016
Role of Aqueous Phase Chemistry, Interfacial Film Properties, and Surface Coverage in Stabilizing Water-in-Bitumen Emulsions
Several factors influencing the stability of asphaltene- and bitumen-stabilized water-in-oil emulsions were investigated including salt type, salt concentration, pH, interfacial film properties, surface coverage, drop size, and emulsion packing. Emulsions were prepared from bitumens (and their asphaltenes) from an oil sands mining process, a cyclic steam process, and a steam-assisted gravity drainage process. The aqueous phases consisted of reverse-osmosis water and salts (NaCl, CaCl2, Na2SO4, KCl, and Na2CO3), and the organic phases consisted of 10 g/L asphaltenes (extracted with n-heptane) or crude oil bitumen dissolved in heptane toluene solutions. The stability of the emulsions was assessed in terms of the percentage of water resolved after repeated treatment cycles involving heating at 60 degrees C and centrifugation at 3500 rpm. The bitumen water systems had similar behavior to the asphaltene-water systems, suggesting that the emulsion stabilizers come primarily from the asphaltenes. Irreversibly adsorbed interfacial films were formed in all cases, a condition necessary for mechanical stabilization. Salt contents as low as 0.02 wt % were found to significantly increase the stability of the emulsions. The increase in stability correlated with an increase in the mass and apparent molecular weight of asphaltenes adsorbed at the interface. A mass surface coverage of 5 mg/m(2) and an apparent molecular weight of 7000 g/mol appear to be the threshold required for stable emulsions.