In this work, a bifunctional model was developed to fit and predict the phase inversion point (PIP) of microemulsions containing polar oils. This model incorporated the hydrophilic−lipophilic difference (HLD) equations, where HLD = 0 at the PIP. The model uses a Langmuir isotherm to account for the interfacial segregation of polar oils as a function of their concentration in the bulk oil phase. The segregated polar oil was treated as being surfactant-like, having a characteristic curvature (Cc). The polar oil in the bulk oil phase was characterized via an equivalent alkane carbon number (EACN). The Cc value was obtained considering deviations in the PIP at low polar oil concentrations. The EACN was determined considering PIP deviations at high polar oil concentrations. Naphthenic acid and dodecanol were used as model polar oils mixed with ionic and nonionic surfactants and nonpolar oils. The EACN of the polar oil was shown to be independent of the EACN of the nonpolar oil and likely independent of the surfactant. The Cc for dodecanol was likely independent of the surfactant used. For naphthenic acid, the Cc was independent of the nonpolar oil, and within a certain surfactant type (ionic, nonionic, or extended ionic), it was likely independent of the surfactant. For the naphthenic acid systems, the segregation predicted via the bifunctional model was consistent with experimental measurements of this segregation. Given that the bifunctional model only involves phase inversion experiments, it is a convenient method to determine the oil-like and surfactant-like nature of polar oils.

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 (ASs) 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 ASs, diluted bitumen, and deasphalted bitumen (maltenes), which led to the realization that ASs 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.

No abstract

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.

Characterization of the behaviour of commercially available non-ionic surfactants has received considerable attention due to their efficacy in a variety of applications. The main challenge in the application of these types of surfactants is that the hydrophilicity of the surfactant varies with concentration and dilution due to the polydispersity of the ethylene oxide groups. The hydrophilicity of a surfactant can be quantified by the characteristic curvature (Cc) parameter of the hydrophilic–lipophilic difference (HLD) framework. In this work, a model based on natural logarithmic regression was developed to calculate the Cc value of commercial surfactants as a function of surfactant concentration by a fast and simple phase scan. The slope of the Cc curve and the measured Cc at a reference concentration were used to develop the model. The Cc values determined with the model agreed with the measured values from the phase scans. Furthermore, the linear mixing rule proved to be reliable for mixtures of polydisperse ethoxylated surfactants. Finally, the impact of the water-to-oil ratio on the Cc was evaluated and the implications were discussed.