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 In unpublished experiments, the vapor-liquid equilibrium (VLE) of the same aromatic compounds was also researched at atmospheric conditions. No significant differences between the previous published limiting separation factors at 100 °C and the unpublished ones at atmospheric conditions could be observed.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 (1x). 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 (∆T e 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.

Approach to the 1-propanol dehydration using an extractive distillation process with ethylene glycol

“…The main feature of this apparatus is its Cottrel circulation pump, which ensures a proper contact between liquid and vapor phases. The device is manufactured by Fischer Labor und Verfahrenstechnik (Germany) and several references to it can be found in literature [19][20][21] were used to carry out the sampling. The experiment ended when two consecutive samples of the liquid phase had the same composition (with a difference of ±0.001 mole fraction) and two consecutive samples of the vapor phase had also the same composition (with a difference of ±0.001 mole fraction).…”

Evaporation behaviour of DMS in an aqueous solution at infinite dilution - a review

“…The activity coefficient shows very high values and, according to eqn , reduces the vapour pressure impact. The same behaviour can be observed for hexanal, 2‐phenyl acetaldehyde and 2‐phenyl ethanol . Hence, it is always the mixture properties in form of an activity coefficient that have to be known in order to allow for evaluations about the evaporation behaviour of a considered aroma compound.…”

“…The literature discloses different data for DMS volatility in an aqueous solution and at infinite dilution as follows: Owing to the particular meaning of DMS for climate balance, as well as for fauna, several publications consider DMS volatility in seawater at a temperature from 0 to about 40 °C . Further values can be found for trials with CDTA (cyclohexandiaminetetraacetic) and CDTA‐Fe(II) solution . The broadest areas are measurements of DMS in aqueous solutions . This is particularly due to the high relevance for the petrochemical sector, where DMS is used during refining and thus has to be removed later on. Regarding the brewing industry, two authors offer work dealing with the DMS problematic . …”

“…• Further values can be found for trials with CDTA (cyclohexandiaminetetraacetic) and CDTA-Fe(II) solution (70). • The broadest areas are measurements of DMS in aqueous solutions (67,69,(71)(72)(73)(74)(75)(76)(77)(78)(79)(80). This is particularly due to the high relevance for the petrochemical sector, where DMS is used during refining and thus has to be removed later on.…”

Die Ausdampfung von Aromastoffen

“…2) [29,30]. Weiterhin ist festzuhalten, dass Rückschlüsse vom Dampfdruck eines Reinstoffs auf Mischungseigenschaften dieses Stoffes nicht zulässig sind.…”