Impact of Asphaltenes and Naphthenic Amphiphiles on the Phase Behavior of Solvent−Bitumen−Water Systems

A limiting factor impacting the quality and recovery of bitumen from oil sand operations is the formation of stable water-in-oil (w/o) and/or oil-in-water (o/w) emulsions during froth treatment. In a previous study, the impact of asphaltene partitioning on oil−water phase separation from the resulting emulsified phases (rag layers) was evaluated as a function of the solvent−bitumen−water ratio, temperature, and solvent aromaticity. In this work, the added effect of naphthenic amphiphiles at concentrations of 3 and 10 wt % on oil−water phase separation from similarly formulated rag layers is assessed. The observed phase behavior of these rag layers is discussed in view of interfacial coadsorption mechanisms proposed in the literature. A major finding is that, under alkaline process conditions, an increase in the concentration of sodium naphthenates (NaNs), produced as a result of naphthenic amphiphile dissociation, promotes a shift in emulsion morphology from w/o to o/w. The resulting transition from asphaltene- to NaN-controlled properties significantly limits oil−water phase separation as a result of an increase in the surface area to volume ratio of dispersed droplets and an enhancement of interfacial asphaltene partitioning. Contrary to NaN-free systems, it was also observed that both the temperature and solvent aromaticity have a minimal effect on the phase behavior of NaN formulations. Furthermore, undissociated naphthenic amphiphiles, referred to as naphthenic acids, are capable of promoting oil−water phase separation under acidic formulation conditions.