Investigation of Coking Propensity of Narrow Cut Fractions from Athabasca Bitumen Using Hot-Stage Microscopy

The incipient mesophase formation of 10 narrow cut fractions from Athabasca bitumen vacuum bottoms boiling above 525 °C (pitch) derived by supercritical fluid extraction (extraction) using pentane was performed using hot-stage microscopy. The experiments were performed in a stream of hydrogen at 750 psi (5.2 MPa) and 440 °C. The formation of mesophase for these pitch fractions correlated with their macromolecular carbon residue, molecular weight, and aromaticity. The higher the values of these properties, the sooner the mesophase appeared. The time for the mesophase formation was the shortest in a pitch fraction containing 88 wt % asphaltenes. In cases where the fractions contained low boiling point materials, the mesophase appeared significantly sooner than expected. This was rationalized in terms of the induction period where certain fractions of heavy oils, if present, delay mesophase formation.