Investigation of subfractions of athabasca asphaltenes and their role in emulsion stability

The ability to stabilize water-in-oil (W/O) emulsions for six studied asphaltene subfractions is dependent on their solubility rather than on their concentration, polarity, molecular weight, or other parameters. Paraffinic froth treatment technology recently introduced in the oil sand industry yields a clean bitumen product (<0.1 wt % water and <0.1 wt % solids) at a solvent-to-bitumen ratio above a critical value, which corresponds to the onset of asphaltene precipitation. Six subfractions of Athabasca bitumen asphaltenes were obtained by precipitation with a gradually increasing heptane-to-bitumen (H/B) ratio, from 1.25 to 40. The properties of the asphaltene subfractions obtained were investigated by elemental analysis, Fourier transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopy, and vapor pressure osmometry (VPO). There were no significant differences in the molecular masses of the six asphaltene subfractions. However, the aromaticity and the metalloporphyrin (vanadyl) content in the asphaltene subfractions systematically decreased as the H/B ratio increased. The first three subfractions had lower H/C ratios, as well as higher metalloporphyrin content, and were less soluble in heptane/toluene (H/T) mixtures. Also, their solubility was more sensitive to the aromaticity of the solvent. The last three subfractions had higher H/C ratios and lower metalloporphyrin content. Their solubility in H/T was greater and less sensitive to the aromaticity of the solvent.