Phase behavior of bitumen and n-pentane

The phase boundaries for mixtures of n-pentane and bitumen were determined at temperatures from 21 to 280 °C and pressures up to 14 MPa. Both vapor-liquid equilibria and liquid-liquid (solvent-rich and asphaltene-rich phases) equilibria were observed for these mixtures. Saturation pressures (vapor-liquid boundary) were measured using both a PVT cell and a blind cell apparatus at temperatures ranging from 90 to 280 °C. The compositions at which a separate asphaltene-rich heavy phase is formed (asphaltene onset point or liquid-liquid boundary) were measured using a high pressure microscope apparatus for a temperature range of 20-180 °C and were extrapolated from asphaltene yield data at temperatures up to 250 °C.At low temperature, the asphaltene-rich heavy phase appears as dispersed glassy particles. However, at temperatures above approximately 140 °C, this heavy phase separates as a continuous liquid and; therefore, a sample of this phase can be isolated and collected. A PVT cell procedure was developed to collect and assay heavy liquid phases in order to determine the asphaltene yield and composition in terms of solvent, maltene, and C5-asphaltene (n-pentane insoluble asphaltenes) contents. A blind cell apparatus was also designed to measure C5-asphaltene yields for multiple samples simultaneously using a similar procedure.The asphaltene yield, (mass of C5-asphaltene partitioning to the heavy phase) was measured for a range of mixtures of bitumen and n-pentane with feed compositions from 50 to 90 mass % n-pentane at temperatures from 21 to 250 °C and pressures up to 13.8 MPa. Heavy phase compositions were measured for feed compositions of 59-72 mass % n-pentane at 180 °C and 4.8 MPa. The ability of a modified Peng-Robinson cubic equation-of-state model to predict the phase boundaries and the yield and phase composition data is assessed.