The potential of head-space gas chromatography for VLE measurements

Abstract

Head-space gas chromatography (HS-GC) is thought to allow the performance of (vapour+liquid) equilibrium (VLE) measurements in a fast and automated way. However, two decades after the first applications of HS-GC for this purpose, the potential of this technique is not fully developed yet. Measurements of isothermal VLE and activity coefficients of mixtures can be obtained in a high throughput scenario. However, several considerations have to be taken into account before starting the analysis, such as the equilibration time or the minimum sample volume and the GC response factors. These aspects can strongly influence on the validity of the results and should therefore be determined for each mixture.In this paper, four azeotropic mixtures of interest in the pharmaceutical and chemical industry, i.e., (ethylacetate+water), which forms a heterogeneous azeotrope, (ethylacetate+isooctane), (acetonitrile+toluene) and the ternary mixture (acetonitrile+toluene+tetrahydrofuran), are considered to show the potential of HS-GC for VLE measurements. The thermodynamic analysis of VLE data leads to activity coefficients for the mixtures at (35, 50, and 70)°C. In addition, the experimental data are compared with thermodynamic models and data from the literature, when available.