Interfacial behavior and partitioning of partially neutralized naphthenic acids: experiments versus HLD-NAC predictions.

Recent studies have shown that naphthenic acids (NAs) and sodium naphthenates dominate the interfacial activity of bitumen and the formation of bitumen emulsions. NAs are naturally occurring mixtures of carboxylic acids in bitumen, where their concentration can reach 4 wt%. Unlike other fatty acid-containing oils, alkaline neutralization of NAs in bitumen does not lead to ultralow interfacial tensions (IFT<0.1 mN/m). Ultralow IFTs are beneficial towards separating emulsions and could be beneficial in the separation of bitumen emulsions. Two possible reasons for the lack of ultralow IFTs with neutralized NAs were explored. One involved insufficient adsorption and neutralization of NA, and the other was the partition of naphthenic species in different phases. Dynamic IFT and pH studies suggest that adsorption and neutralization of NA proceed as predicted by the stoichiometry of the reaction. On the other hand, it was determined that a large fraction of the sodium naphthenates (NaNs) formed at the interface partitioned back into the oil. By forcing the participation of NaNs at the interface via their introduction through the aqueous phase, it is possible to create transient ultralow IFTs. The conditions (NA and NaN concentration and the salinity of the system) that led to ultralow IFTs were predicted by an HLD-NAC model previously validated for the neutralization of oleic acid.