Unusual Retrograde Condensation and Asphal Tene Precipitation in a Model Heavy Oil

A partial phase diagram for the system athabasca bitumen vacuwn bonoms (ABVB) (24.6 wt. % / 2 mole %) + dodecane (73.8 wt. % / 47 mole %) + hydrogen (1.6 wt % /51 mole %) was constructed in the temperature range 425 K to 725 K and the pressure range 2 MPa to 7 MPa using an X-ray view cell apparatus. This t1uid system is shown to exhibit two phase LIV and three phase LIL2V phase behaviour over parts of this poT region. The shape of the low temperature boundary between the LIV and L IL2 V zones is characteristic of dilute asymmetric mixtures where a heavy liquid phase. L2, appears then disappears within the light liquid phase. L" on isothermal compression. Such phase behaviour is referred to as unusual retrograde condensation and is of both practical and theoretical interest. Transitions between the multi phase regions were found to be reversible at temperatures less than 660 K. in all cases. At higher temperatures irreversible "asphaltene precipitation" arose within the L2 phase. "Asphaltene precipitation" did not arise in the absence of the L2 phase. i.e.: within the LIV region. even at temperatures in excess of 700 K. These data provide a strong link between "asphaltene precipitation" and multi phase behaviour. and demonstrate a physical rather than kinetic basis for asphaltene precipitation at elevated temperatures.