A Systematic and Consistent Approach to Determine Binary Interaction Coefficients for the Peng-Robinson Equation of State

Abstract

Summary A new technique to determine binary interaction coefficients for a cubic equation of state (EOS) is introduced. The technique is physically consistent and easy to apply when an EOS is tuned to laboratory-measured PVT data. The method's simplicity provides a rational way of evaluating the sensitivity of binary interaction coefficients to fluid composition and temperature. Laboratory-measured expansion data are demonstrated to be crucial for proper determination of binary interaction coefficients for near-critical fluids. The ability of the technique has been demonstrated by matching laboratory-measured constant-composition-expansion curves for six fluid compositions, including black-oil, volatile-oil, rich-gas-condensate, and lean-gas-condensate systems. In addition, the near-critical fluid behavior has been evaluated by matching constant-composition-expansion data for a fluid at four temperatures in the near-critical range, two on either side of the critical temperature. The literature reports that the Peng-Robinson EOS (PR-EOS) cannot predict the retrograde phase behavior of the rich-gas-condensate fluids applied in this study. This paper shows that this is because insufficient and/or improper binary interaction coefficients were used in the fluid characterization. The method enables tuning of near-critical fluid behavior in addition to normal bubblepoint and dewpoint system behavior. Use of the proposed procedure to assign binary interaction coefficients may allow matching of renascent condensation for a near-critical bubble-point system.