(63b) Reversible and Irreversible Phase Transitions in Athabasca Bitumen Asphaltenes

The precipitation of asphaltenes causes severe fouling problems throughout the production, transport and refining operations of oil companies worldwide. The economic impact is significant. Examples include plugging and wettability reversal in reservoirs, to catalyst and heat exchanger fouling in refineries leading to production failure or production loss in the first example and to more frequent refinery shutdowns in the second example. Asphaltenes are a poorly understood petroleum fraction and there is a critical need of quantitative prediction tools and data related to there thermophysical properties. In this work, the phase behaviour of Athabasca asphaltenes separated from their native hydrocarbon resource using normal alkanes was studied using a combination of differential scanning calorimetry (DSC), temperature modulated differential scanning calorimetry (TMDSC) and rheology measurements in the temperature interval 200 K to 520 K. For pentane through dodecane Athabasca asphaltenes, there is a broad reversible endothermic phase transition, from solid to liquid, overlapping an irreversible exothermic phase transition in the temperature range 330 K and 520 K. Thus, in general, asphaltene thermal and physical properties and hence phase behaviour differ depending on their thermal history in this temperature range. This result may account for the diversity of asphaltene behaviors in apparently similar industrial environments.