Viscosity of Canadian Oilsands Bitumen and Its Modification by Thermal Conversion

The dependence of the viscosity of Canadian oilsands-derived bitumen on different factors such as the microstructure, chemical composition, compatibility, and interactions among the different constituent components has been documented in the literature, but a comprehensive review is lacking. The goal of this chapter is to explore, in depth, the sensitivity of the viscosity of bitumen to some of these parameters and to provide a scientific explanation for the observed changes. Noncatalytic thermal conversion is used as a tool for realizing this objective. Previous studies on the thermal treatment of bitumen reported contrasting trends in viscosity with reaction time, but a substantial explanation was not provided; this served as a motivation for the experimental investigations in this chapter. Specifically, details of the postreaction procedures, including the nature of the solvent used to extract the products from the reactor and the rheological conditions, such as shear rate, used for viscosity measurements, had a significant impact on viscosity. Because some solvent remained after evaporation, methylene chloride introduced hydrogen-bonding interactions, which plausibly increased the viscosity of the thermally converted bitumen significantly. This effect was not observed with toluene as the extraction solvent. The tracking of changes in other properties, such as free-radical content, boiling-point distribution, and aromatic and aliphatic contents, during thermal conversion and before and after solvent addition and removal assisted in explaining the viscosity changes. The chemical composition of the feed and its geological origin also seems to have an effect on its viscosity. Assuming a colloidal representation for bitumen, we propose a theory on the effect of the nature of asphaltene aggregation on viscosity in terms of changes in the effective volume of the aggregate clusters during thermal conversion.