GE Models and Algorithms for Condensed Phase Equilibrium Data Regression in Ternary Systems: Limitations and Proposals

Abstract

Phase equilibrium data regression is an unavoidable task necessary to obtain the appropriate values for any model to be used in separation equipment design for chemical process simulation and optimization. The accuracy of this process depends on different factors such as the experimental data quality, the selected model and the calculation algorithm. The present paper summarizes the results and conclusions achieved in our research on the capabilities and limitations of the existing G E models and about strategies that can be included in the correlation algorithms to improve the convergence and avoid inconsistencies. The NRTL model has been selected as a representative local composition model. New capabilities of this model, but also several relevant limitations, have been identified and some examples of the application of a modified NRTL equation have been discussed. Furthermore, a regression algorithm has been developed that allows for the advisable simultaneous regression of all the condensed phase equilibrium regions that are present in ternary systems at constant T and P. It includes specific strategies designed to avoid some of the pitfalls frequently found in commercial regression tools for phase equilibrium calculations. Most of the proposed strategies are based on the geometrical interpretation of the lowest common tangent plane equilibrium criterion, which allows an unambiguous comprehension of the behavior of the mixtures. The paper aims to show all the work as a whole in order to reveal the necessary efforts that must be devoted to overcome the difficulties that still exist in the phase equilibrium data regression problem.

Comments on the correlation of vapor–liquid equilibrium (VLE) data in azeotropic ternary systems

“…Regarding practical and engineered oriented results, it is important to emphasize that better results are not always accomplished with the apparently superior models, as we showed [23] …”

Liquid-liquid equilibrium for the ternary system ethanol/toluene/n-decane: a correction to the existing coexistence curve and NRTL parameters

“…Considering that Equation (1) is the dominant regression technique, it is expected and indeed found that many reported ternary parameters are thermodynamically inconsistent [4]. This is because, as discussed earlier, Equation (1) is only a necessary condition, which does not ensure that the solution is a global minimum.…”

“…Since there are numerous compositions that are able to satisfy the iso-activity criterion with a small residual, inconsistent solutions are often obtained [4]. Thus, the iso-activity criterion must be enforced with an absolute residual of at most 10 −4 to obtain a consistent solution.…”

The Potential of Non-Ionic Surfactants for Extraction of Lactic Acid from Aqueous Solution

“…The suitability of the surfactant as solvent for lactic acid extraction can be initially assessed by the type of the ternary system. The results indicated that all the systems studied belong to the Type 1 Treybal classification of ternary systems [35], with the water-surfactant binary pair exhibiting partial immiscibility. It is important to note that all the surfactants used in this study are mixtures containing different lengths of the alcohol component.…”