Zipper-like linker self-assembly to obtain low interfacial tensions with partially neutralized naphthenic acids.

The presence of naphthenic acid in crude oil is considered one of the most important factors in the formation and stabilization of water in bitumen emulsions. While naphthenic acids (NAs) are oil-soluble lipophilic amphiphiles, their neutralized form, sodium naphthenates (NaNs), has highly hydrophilic components. The right NA/NaN proportion should produce a balanced, net-zero curvature at the oil-water interface, leading to ultra-low interfacial tensions (IFTs<0.1 mN/m). A previous study showed that such an expectation is not achievable in model oil systems with NA and NaN, likely because of the partition of NA and NaN species. This work explores the hypothesis that it is possible to achieve ultralow IFTs using surfactants with balanced hydrophilic-lipophilic interactions that can trigger a "zipper-like" self-assembly of hydrophilic and lipophilic amphiphiles at the interface. A second hypothesis is that by producing these ultralow IFTs one can achieve fast dewatering of emulsions of oil containing partially neutralized NAs. After introducing sodium dihexyl sulfosuccinate (SDHS) and sodium dioctyl sulfosuccinate (Aerosol OT or AOT) as balanced surfactants, it was noted that one could produce ultralow IFTs in partially neutralized NAs. Using the hydrophilic-lipophilic difference (HLD) and net-average curvature (NAC) framework, it was possible to reproduce the experimental trends when using appropriate values for the critical micelle concentration (CMC) for NaN and SDHS. The best zipper assembly performance was obtained when the intrinsic HLD of the balanced surfactant is near zero. Under those conditions, it was possible to find ultralow IFTs and fast dewatering of emulsions with NA content and pH relevant to diluted bitumen emulsions obtained during naphthenic froth treatment.