Limiting Separation Factors and Limiting Activity Coefficients for Hexanal, 2-Methylbutanal, 3-Methylbutanal, and Dimethylsulfide in Water at (98.1 to 99.0) °C

Abstract

This work is a continuation of preceding work in which limiting separation factors of important wort flavor components in water at 100 °C were determined. In unpublished experiments, the vapor-liquid equilibrium (VLE) of the same aromatic compounds was also researched at atmospheric conditions. No significant differences between the previous published limiting separation factors at 100 °C and the unpublished ones at atmospheric conditions could be observed. Because of this fact, the results of the measurements were used to calculate residue curves during the atmospheric boiling of wort. This study was only investigated at atmospheric conditions. A recirculating Gillespie-type still was used to determine the limiting separation factor (K∞) for hexanal (x), 2-methylbutanal (x), 3-methylbutanal (x), and dimethylsulfide (x) in water (1 - x). Since the solutions were highly dilute (x < 10 -6 ), infinite dilution was assumed. As the investigated components do not have large absorbances in the UV region, they could not be analyzed by UV spectroscopy. Therefore, in contrary to the preceding work, they were analyzed by gas chromatography. As the boiling point of the solution only changed slightly at the given atmospheric conditions (ΔT ≤ 0.9 °C), the limiting separation factors were acquired assuming a constant average temperature of 98.55 °C. Thus, limiting activity coefficients were calculated at the same average temperature. The calculated limiting activity coefficient depends highly on the reliability of the vapor pressure data of the pure components.