Simulation of the phase behaviour of Athabasca vacuum residue + n-alkane mixtures

Phase behaviour measurement and prediction for ill-defined hydrocarbons such as vacuum residue + light hydrocarbons present significant challenges, from view-cell design and operation, to thermolysis reactions at high temperature to fluid speciation and phase stability analysis during equilibrium calculations. In a prior contribution, simulated phase behaviour results for Athabasca vacuum residue + n-decane mixtures based on the Peng–Robinson equation of state were presented. In that work, Athabasca vacuum residue pseudo components that were identified exogenously and parameters for the model were computed from these pseudo components using the Marrero and Gani group contribution method. Here, this thermodynamic model is extended to include Athabasca vacuum residue + n-alkanes from n-pentane to n-dodecane. Only binary interaction coefficient values between residue pseudo components and n-alkanes were tuned. Densities of co-existing liquid phases present in the three-phase regions are calculated and compared to the experimental data for AVR + n-decane. The simulations are in qualitative and quantitative agreement with measurements over a broad ranges of temperature, pressure, and composition. The results presented in this contribution illustrate the reliability of the proposed thermodynamic modeling approach and its potential use as a universal heavy oil modeling tool for the simulation of paraffinic deasphalting, separation and refining processes for ill-defined hydrocarbon mixtures.

► Phase diagrams for Athabasca bitumen + n-alkanes were simulated.
► The phase behaviour was simulated using a group contribution equation of state.
► The vacuum residue was characterized using chemical composition, and related data.
► Group contribution offers advantages over refinery-based characterization.
► The results illustrate the potential of the approach but additional development is required.