Department of Chemical Engineering, Process Engineering for Sustainable Systems (ProcESS), KU Leuven, W. de Croylaan 46, B-3001 Leuven, Belgium.
J Chromatogr A. 2013 Aug 9;1302:111-7. doi: 10.1016/j.chroma.2013.06.007. Epub 2013 Jun 14.
Head-space gas chromatography (HS-GC) is an applicable method to perform vapor-liquid equilibrium measurements and determine activity coefficients. However, the reproducibility of the data may be conditioned by the experimental procedure concerning to the automated pressure-balanced system. The study developed in this work shows that a minimum volume of liquid in the vial is necessary to ensure the reliability of the activity coefficients since it may become a parameter that influences the magnitude of the peak areas: the helium introduced during the pressurization step may produce significant variations of the results when too small volume of liquid is selected. The minimum volume required should thus be evaluated prior to obtain experimentally the concentration in the vapor phase and the activity coefficients. In this work, the mixture acetonitrile-toluene is taken as example, requiring a sample volume of more than 5mL (about more than 25% of the vial volume). The vapor-liquid equilibrium and activity coefficients of mixtures at different concentrations (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 molar fraction) and four temperatures (35, 45, 55 and 70°C) have been determined. Relative standard deviations (RSD) lower than 5% have been obtained, indicating the good reproducibility of the method when a sample volume larger than 5mL is used. Finally, a general procedure to measure activity coefficients by means of pressure-balanced head-space gas chromatography is proposed.
顶空气相色谱（HS-GC）是一种适用于进行汽液平衡测量和确定活度系数的方法。然而，数据的重现性可能受到与自动压力平衡系统相关的实验程序的影响。本工作中开展的研究表明，为了确保活度系数的可靠性，小瓶中液体的最小体积是必要的，因为它可能成为影响峰面积大小的参数：在加压步骤中引入的氦气可能会导致当选择的液体体积太小时，结果产生显著变化。因此，在实验获得气相浓度和活度系数之前，应评估所需的最小体积。在这项工作中，以乙腈-甲苯混合物为例，需要的样品体积超过 5mL（约为小瓶体积的 25%以上）。已确定了不同浓度（0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9 摩尔分数）和四个温度（35、45、55 和 70°C）下的汽液平衡和活度系数。得到的相对标准偏差（RSD）低于 5%，表明当使用大于 5mL 的样品体积时，该方法具有良好的重现性。最后，提出了一种通过压力平衡顶空气相色谱法测量活度系数的通用程序。
