Refractive index measurements of diluted bitumen solutions

The objective of this study was to obtain estimates for the refractive indices of bitumen, maltenes, and asphaltenes. Refractive index measurements performed on various bitumen–solvent mixtures were analyzed using a mixing model that related the refractive index of an ideal mixture to the refractive indices of the pure components of the mixture. Measurements could only be obtained for bitumen–solvent mixtures ranging in bitumen volume fraction from 0 to about 0.50. Extrapolation to a volume fraction of unity provided estimates of 1.584, 1.571 and 1.708 for the refractive indices of bitumen, maltenes, and asphaltenes, respectively. A precipitating solvent was also used to show that the onset of asphaltene precipitation could be detected from refractive index measurements. For a mixture of heptane and bitumen, the onset of asphaltene precipitation appeared to occur at a bitumen volume fraction of about 0.32.