Characterizing the Behavior of Bitumen-Water Systems with the Hydrophilic-Lipophilic Difference (HLD) Framework

Emulsions of water in bitumen, even in solvent-diluted bitumen, are notorious for their stability. Such stability affects the removal of water in the Froth Treatment Process prior to upgrading of bitumen extracted from mining operations. The literature presents various examples of the use of the Hydrophilic-Lipophilic Difference (HLD) framework to formulate demulsifiers for conventional crude oils, reducing the emulsion stability from hours to minutes when HLD=0 (phase inversion point). To apply this approach to bitumen emulsions, the HLD of these systems needs to be assessed. A previous attempt to obtain the HLD of bitumen emulsions was incomplete because the suspected surfactant-like and oil-like behavior of polar oils in bitumen, particularly asphaltenes and naphthenic acids (NAs), could not be resolved. This question was revisited using a newly established framework for the HLD of polar oils. To this end, microemulsion phase behavior studies were conducted involving mixtures of ionic and nonionic surfactants with asphaltenes, diluted bitumen, and deasphalted bitumen (maltenes), which led to the realization that asphaltenes do not play a role in HLD when other surfactants are present in the system. Instead, NAs and their dissociation into naphthenates dominate the phase behavior of bitumen emulsions. It was determined that a gradual change in the degree of dissociation of NAs, induced by sodium hydroxide addition, could substantially change the HLD of the system and the accompanying changes in interfacial tension, emulsion stability, and residual water content in the oil phase.