A comprehensive comparison of mixing rules for calculation of phase equilibria in complex systems

Five different mixing rules for the SRK-EOS have been investigated for phase equilibrium calculations in chemically complex systems at high pressures. The mixing rules are those of van der Waals with two binary parameters, the Huron-Vidal rule with three binary NRTL-parameters, the MHV2-model with UNIFAC-group parameters, the Schwarzentruber - Galivel-Solastiouk - Renon rule with three binary parameters, and the density dependent local composition rule with three binary parameters. The mixing rules are investigated both with and without temperature-dependent parameters. For each mixing rule the parameters are estimated using binary data for systems containing H₂O, CO₂, N₂, H₂S, CH₃OH and n-alkanes up to n-decane. With the estimated parameters, multicomponent data have been predicted and compared with experimental results. Furthermore the influence of the thermodynamic consistency of the binary data has been investigated.There is found a large discrepancy in the predicted results for multicomponent phase equilibria between the different mixing rules, although almost the same results are obtained for the correlation of the binary data. For the investigated systems, the Huron-Vidal model gives the best overall predictions. If temperature dependent parameters are used, it is necessary to be very careful when extrapolation of temperature is performed.