André Péneloux

A consistent correction for Redlich-Kwong-Soave volumes

Abstract If the volumetric and phase behaviour of a fluid mixture is calculated by means of an equation of state, certain translations along the volume axis may be effected that leave the predicted phase equilibrium conditions unchanged. This property may be exploited in the form at a consistent correction to improve volume estimations by the Redlich-Kwong-Soave method. Applications of this improved method to pure liquids, mixtures of liquids or gases, and petroleum fluids show that markedly superior volume estimations are obtained, except in the neighbourhood of the pure-component critical points; nonetheless, critical volumes for mixtures can be estimated correctly.

Excess functions and equations of state

Abstract In an extension of the development originally presented by Vidal, the connection between excess functions and equations of state is established by equating excess functions derived from the Guggenheims quasi-lattice theory to expressions derived from equations of state. The zeroth approximation of that theory is shown to be compatible with the classical van der Waals mixing rules, which may be a starting point for interesting methods founded on excess functions for correlating and predicting thermodynamic properties of fluids.

Group-contribution equation of state for correlating and predicting thermodynamic properties of weakly polar and non-associating mixtures: Binary and multicomponent systems

Abstract Abdoul W., Rauzy E. and Peneloux A., 1991. Group-contribution equation of state for correlating and predicting thermodynamic properties of weakly polar and non-associating mixtures. Binary and multicomponent systems. Fluid Phase Equilibria, 68: 47-102. The applicability of the “Guggenheim quasi-lattice excess function equation of state” formalism is tested through a zeroth approximation group-contribution model and a Peng-Robinson-type equation of state. The temperature-dependent correlations of the group-contribution model are derived from low-pressure excess enthalpy (HE) and vaporliquid equilibrium (VLE) binary data and are then extended to the prediction of high-pressure vapor-liquid equilibria of mixtures of weakly polar and non-associating compounds (i.e. hydrocarbons, CO2, H2S, N2). The numbers of binary systems, data sets and determinations used in the development and testing of the method are 169, 805 and 10634 for low-pressure VLE; 282, 789 and 11308 for HE; and 163, 1329 and 12272 for high-pressure VLE, respectively. The average relative deviation with experiment in bubble-point pressure is 1% and the average absolute deviation in vapor-phase composition is 0.005 for low-pressure VLE data. Heat effects are well reproduced with average deviations of 12 J for 7009 determinations of binaries with HE less than 300 J and 5.5% for 4299 determinations of binaries with higher HE. Owing to a term accounting for chain-length effects, the accuracy of the prediction of high-pressure VLE is not deteriorated by the group-contribution approach (average deviations of 3% in bubble-point pressure, 0.0103 in vapor-phase composition). Thus, in addition to its predictive power, the method is found to be an improvement over the classical Peng-Robinson procedure with constant binary interaction parameters, especially for mixtures of molecules of different sizes.

A new ebulliometric technique. Vapour-liquid equilibria in the binary systems ethanol-n-heptane and ethanol-n-nonane

Abstract Berro, C., Rogalski, M. and Peneloux, A., 1982. A new ebulliometric technique. Vapour-liquid equilibria in the binary systems ethanol-n-heptane and ethanol-n-nonane. Fluid Phase Equilibria, 8: 55–73. This paper considers a modification to a recirculation still described previously by Berro et al. (1975). The ebulliometric apparatus is coupled to a closed flow system allowing continuous densimetric analysis of liquid and vapour phase compositions. Vapour-liquid equilibria have been measured for two systems: ethanol-n-heptane, at 303.27 (T-P-x data only) and 343.17 K; and ethanol-n-nonane, at 343.21 K. The experimental data were reduced using the observed-deviation method (Neau and Peneloux, 1981). The results of the reduction are presented and discussed.

Estimation of model parameters. Comparison of methods based on the maximum likelihood principle

Abstract Neau, E. and Peneloux, A., 1981. Estimation of model parameters. Comparison of methods based on the maximum likelihood principle. Fluid Phase Equilibria, 6: 1–19. Two methods based on the maximum likelihood principle are investigated for the estimation of model parameters from experimental data: the estimated deviation method of Jacq et al. (1979) and Anderson et al. (1978) and the observed deviation method of Peneloux et al. (1975, 1976), Sutton and MacGregor (1977) and Patino-Leal (1979). It is shown that these two methods, which differ in the size of matrices used and in the way of weighting the data, lead to the same values for the model parameters. It is also shown that results do not depend on the fitted functions when an appropriate weighting method is used. The interest of the observed deviation method is discussed. Theoretical results are illustrated in the reduction of binary vapour—liquid equilibrium data.

Vapour-liquid equilibria calculations for normal fluid systems using a new cubic equation of state

Abstract Freze, R., Chevalier, J.-L., Peneloux, A. and Rauzy, E., 1983. Vapour-liquid equilibria calculations for normal fluid systems using a new cubic equation of state. Fluid Phase Equilibria, 15: 33–66. A new cubic equation of state is presented with a pseudocritical compressibility factor taken as substance-dependent. This equation leads to good phase-behaviour prediction for normal fluid mixtures up to the critical state, even in the case of binary systems involving a light and a heavy alkane, for which the equations of Redlich-Kwong-Soave and Peng-Robinson give poor results. With the volume correction proposed by Peneloux et al., this method also gives good estimates of the volumetric properties of pure compounds and mixtures, except in the neighbourhood of the pure-component critical points.

Modelling of the phase behaviour of mixtures in the critical region using the augmented Peng-Robinson equation of state

Abstract The Peng-Robinson equation extended to the PVT property representation in the critical point neighbourhood (PRA equation) was used to calculate binary pressure-composition and pressure-density diagrams. The modified excess function at constant packing fraction model was used to take into consideration binary interactions. In the case of binary systems exhibiting the mixture critical point, calculation results were satisfactory and substantially improved with respect to those obtained using the volume corrected Peng-Robinson (PRC) equation.

Variance analysis fifteen years ago and now

Abstract Conditions for applying the maximum likelihood principle for data reduction are reviewed. Methods based on variance analysis allow estimation of model parameters, reduction of isothermal VLE data and modelling of petroleum fluids.

Use of heat capacities for the estimation of cubic equation-of-state parameters-application to the prediction of very low vapor pressures of heavy hydrocarbons

Abstract Improvement in the prediction of very low vapor pressures is checked by introducing heat capacity data into the estimation of cubic equation-of-state (EOS) parameters. As the key parameter is the temperature-dependent parameter a, several expressions (mainly of exponential form) were investigated. All of them were chosen in order to show a consistent behavior for the two considered properties (vapor pressures and heat capacities). The cubic EOS used as an illustration is of the Peng–Robinson type applied to heavy hydrocarbons. No satisfactory refinement in the prediction of the very low vapor pressures was observed in comparison with the results obtained by extrapolating the EOS from medium to very low pressures. This work has, however, the following benefits: (1) to point out the changes that should be made to improve these predictions; (2) to inform on the accuracy that may be obtained if vapor pressures of heavy organic compounds are predicted from heat capacity data as the sole alternative for estimating the temperature-dependent parameter a of a cubic EOS; (3) to confirm the reliability of the cubic group-contribution (GC)-based EOS proposed by Coniglio et al. [Ind. Eng. Chem. Res. 39 (2000) 5037] when extrapolated for modeling crude oils or gas condensates encountered in the petroleum industry.