For the evaluation of autosolvent effect of bitumen, thermal cracking characteristics of bitumen is discussed from conversion and chemical structure changes. Athabasca tar sand bitumen was separated into light and heavy fractions by distillation. Mixtures of the both fractions at various ratios were heat-treated at 693K under 10MPa of nitrogen for 60min. Conversion of the heavy fraction into the light fraction was calculated with the chemical structure changes based on thermogravimetric analysis, elemental analysis and ^1H-NMR. Negative effect of the light fraction on the heavy fraction cracking was observed with dealkylation and paraffin formation. Polymerization of the light fraction to the heavy fraction was suggested due to lack of hydrogen in the thermal cracking under nitrogen atmosphere.
