Critical parameters optimized for accurate phase behavior modeling for heavy n-alkanes up to C100 using the Peng–Robinson equation of state

The Peng–Robinson equation of state (PR EOS) is widely used for modeling phase behavior of hydrocarbon mixtures. When applied to heavy hydrocarbons and their mixtures, however, the PR EOS can exhibit erroneous phase behavior predictions. In this research, we develop new correlations for critical temperatures (TC), critical pressures (PC), and acentric factors (ω) that enable the PR EOS to accurately predict phase behavior of n-alkanes up to C100.Predictions using the PR EOS with the new correlations give 3.0% average absolute deviation (AAD) for 3583 density data, and 3.4% AAD for 1525 vapor pressure data for n-alkanes from C7 to C100. Significant improvement is also observed for bubble point pressure and density predictions for n-alkane mixtures. The new correlations developed for TC, PC, and ω are then applied for characterizing 25 different reservoir oils. Results show that, compared to the conventional critical parameter correlations in the literature, our correlations give more accurate phase behavior predictions while requiring less adjustment of the parameters. The optimum TC and PC developed for n-alkanes can serve as useful lower limits for TC and PC of pseudo components of reservoir oils that are characterized using the PR EOS.

► Optimum critical parameters for n-alkanes are developed for the Peng–Robinson EOS. ► New correlations are developed based on the optimum critical parameters. ► Phase behavior of n-C7–100 is accurately predicted with the new critical parameters.