Estimation of Liquid−Liquid−Vapor Equilibria Using Predictive EOS Models. 1. Carbon Dioxide−n-Alkanes

Abstract

This study looks for the first time at the possibility of predicting liquid−liquid−vapor equilibria without preliminary resource to experimental data. For this purpose, the two most successful G E-based semipredictive models (PSRK and LCVM) and the global phase diagram (klGPD)-based semi-predictive approach (GPDA) have been implemented and compared. Although G E-based models require a significant amount of experimental data for evaluation of their parameters and prediction of the equilibrium, GPDA needs no more that 2−3 key experimental points. The superiority of GPDA, which considers the entire thermodynamic phase space, over the G E-based models, which are based on the fit of VLE data, is clearly demonstrated. Although the G E-based models fail to predict global phase behavior and to describe three-phase data accurately, GPDA yields exact predictions of the global phase behavior and accurate estimations of the composition and density of the vapor and the CO2-rich phases. In addition, it is accurate in describing the P−T projection of three-phase lines. All of the models considered are unable to predict the hydrocarbon-rich phase accurately. Presently, this problem cannot be solved without violating the predictive character of the model.

High-pressure phase equilibria in the (carbon dioxide+1-hexanol) system

“…As can be seen, the agreement between the experimental data and the calculations is good, except for the UCEP, which is slightly over predicted, because no restrictions were imposed to precisely obtain the UCEP. It is known that a single set of parameters, even temperature dependent, can not represent well the VLLE line [6,[25][26][27]. The compositions of the two liquid phases as a function of temperature, along the LLV line and the prediction results are illustrated in figure 4.…”

Estimation of Liquid−Liquid−Vapor Equilibria in Binary Mixtures of n-Alkanes

“…Such shapes of the LLVE regions are probably characteristic of both G E -based models because similar results have been described before for the homologous series carbon dioxide-n-alkanes. 3,5 For the latter series in particular, PSRK predicts an almost square-shaped LLVE region. The very close location of TCP and DCEP predicted by this model has also avoided from this model the possibility of describing the characteristic curvature of the end-point lines around the DCEP.…”

Modeling of Trifluoromethane (R-23) or Hexafluoroethane (R-116) and Alkane Binary Mixtures using the Group-Contribution with Association Equation of State

“…Several authors have recognized the importance of considering the comprehensive phase behavior in order to develop predictive thermodynamic models and have made efforts to describe the phase behavior transition of homologues series using group-contribution models, , generalized correlations, − or transferable parameters. , Most of the efforts have been applied to mixtures involving carbon dioxide, with a notable exception being the work of Polishuk who studied the tetrafluoromethane + alkanes homologues series. Nonetheless, to our knowledge, a comprehensive study of the homologues series involving R-23 or R-116 has not been done so far.…”