Experimental vapor–liquid equilibrium (VLE) data, and the activity coefficient model parameters obtained by their correlation, are frequently used in separation processes design. The inspection of this information for ternary systems has revealed some problems that are not widely known and could lead to serious mistakes. A small sampling of ten ternary systems, with VLE data sets at constant pressure, arbitrarily selected has been considered to illustrate these problems. The experimental VLE data and the NRTL model parameters for these systems have been taken from different sources, one database and two commercial simulation packages. A MATLAB code has been developed to prepare 3D graphs where the T/x and T/y surfaces calculated by the activity coefficient model (NRTL) are represented along with the experimental VLE data. The results of the analysis of this small sample are very worrying. In fact, half of the selected systems present severe inconsistences between the experimental VLE data and the T/x,y surfaces calculated using the correlation results published or implemented in the simulation software. These inconsistences are of different natures, but the most notable is the existence of parameter sets that do not correlate at all the VLE behavior of the system that they supposedly represent. These irregularities may occur only in the ternary region, only in the binary subsystems, or, in some cases, in both. These problems go frequently unnoticed for different reasons. As discussed in this work, the typical 2D graphs and deviations in T or P and vapor composition are not enough in some cases so as to have an adequate idea of both the quality of the data and the suitability of the model to represent them. This is particularly true when considering, as is strongly advisible, the complete set of data, i.e. the ternary and binary VLE data simultaneously. Some recommendations are presented in this work to overcome the problems detected both when planning the experimental design to determine VLE data and to correlate them with a model.

中文翻译：

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三元系统中的汽液平衡分析，以充分规划其实验测定和关联

实验气液平衡（VLE）数据以及通过其相关性获得的活度系数模型参数经常用于分离过程设计。对三元系统的这些信息的检查发现了一些不为广泛所知的问题，并且可能导致严重错误。任意选择的十个三元系统的小样本（具有恒压下的 VLE 数据集）已被考虑来说明这些问题。这些系统的实验 VLE 数据和 NRTL 模型参数取自不同来源：一个数据库和两个商业模拟包。已开发了 MATLAB 代码来准备 3D 图形，其中通过活动系数模型 (NRTL) 计算的T / x和T / y表面与实验 VLE 数据一起表示。这个小样本的分析结果非常令人担忧。事实上，一半选定的系统在实验 VLE 数据与使用仿真软件中发布或实现的相关结果计算出的T / x、y表面之间存在严重不一致。这些不一致具有不同的性质，但最值得注意的是参数集的存在，这些参数集与它们所代表的系统的 VLE 行为完全不相关。这些不规则性可能仅发生在三元区域、仅发生在二元子系统中，或者在某些情况下同时发生在两者中。由于不同的原因，这些问题经常被忽视。正如本工作中所讨论的，在某些情况下，典型的 2D 图表以及T或P和蒸汽成分的偏差不足以充分了解数据的质量和代表它们的模型的适用性。当考虑完整的数据集（即同时考虑三元和二进制 VLE 数据）时尤其如此（强烈建议这样做）。这项工作提出了一些建议，以克服在规划实验设计以确定 VLE 数据并将其与模型关联时发现的问题。