X. Y. Zou[1], Xiaohui Zhang and John M. Shaw
Department of Chemical and Materials Engineering
University of Alberta
The phase behavior of Athabasca vacuum bottoms (ABVB), a 798.15 + K boiling fraction of bitumen comprising 32 wt. % pentane asphaltenes, + pentane mixtures is elucidated over the temperature range 293 K to 613 K and the pressure range from sub-atmospheric to 30 MPa. This asymmetric mixture, a model for the development of novel production and refining technologies for heavy oil and bitumen, exhibits complex phase behaviors including both expected (L1L2V) and unexpected (L2L3V) phase behavior separated by a small L1L2L3V zone. Observed bulk phase behaviors are shown to be reversible at temperatures up to 613 K. Experimental pressure-temperature at constant composition phase diagrams, and qualitative pressure-composition at constant temperature phase diagrams are presented. Details of the experimental techniques used to detect critical phenomena and phase boundaries are described. Limited phase behavior data sets for ABVB + heptane, decane and dodecane mixtures, which show systematic phase transitions for ABVB + alkane mixtures as the size of the alkane component is increased, are also discussed. Solid-fluid phase boundaries and deposit formation boundaries in these mixtures remain poorly defined due to ambiguities in the interpretation of experimental data and the small mass fractions involved.
[1] X.-Y. Zou is now working at DBR Oilphase, Edmonton, Alberta, XZou@edmonton.oilfield.slb.com