PERFORMANCE OF CUBIC EOS AT HIGH-PRESSURES

This paper presents an evaluation of the performance of cubic equation s of state in the prediction of the phase behavior of hyperbaric mixtu res. It points out a number of problems that should be resolved in a c ooperative way. Items related to EoS parameter definitions such as int eraction coefficients, critical properties of hydrocarbon compounds an d volume translation are investigated. VLE experimental data, isotherm al flash compositional and volumetric data up to 4000 bar as well as P VT data up to 2000 bar for binary mixtures and synthetic multicomponen t systems have been considered in this study. Correlation and predicti on results are presented with the translated and modified Peng-Robinso n (t-mPR) EoS. It is shown that serious problems are encountered at hi gh pressure, when extrapolated interaction coefficients are used. Pred iction of saturation pressures of gas condensates is more satisfactory when binary interaction parameters are obtained from high pressure de w point correlations. Compositional and volumetric predictions are rem arkable under the assumption that definition of the EoS parameters is based on high pressure VLE binary data. Contradictory results are obta ined with different methods for estimating the critical properties of high molecular weight hydrocarbons. Generalized expressions for the vo lume translation appear to be very efficient even at very high tempera tures and pressures (up to 2000 bar).