Evaluation of a Variation of the Differential Scanning Calorimetry Technique for Measuring Boiling Points of Binary Mixtures at Subatmospheric Pressures

Abstract

Boiling points and vapor–liquid equilibrium (VLE) data are crucial for improving modeling and process design. Therefore, considering the experimental determination of these primary thermodynamic properties, a nontraditional technique that has been under study and has shown some advantages is the differential scanning calorimetry (DSC) technique and its variations. Following a previous work focused only on pure compounds, in this work a set of experiments was performed to evaluate in a systematic way the suitability of its suggested variation of the DSC technique for binary mixtures. Its optimized condition for heating rate (24.52 K·min–1) and sample size (4.6 ± 0.5) mg was used at 4.97 kPa with u(P) = 0.12 kPa for 15 different combinations of n-paraffins and/or fatty alcohols (1-alcohols) in binary mixtures (n-paraffin + n-paraffin, 1-alcohol + 1-alcohol, and n-paraffin + 1-alcohol), taking into account the difference between the boiling points (T b) of the pure compounds at the selected pressure (7 to 63 K). Experiments were configured using the equimolar condition, and pursued effects of this difference on the measured extrapolated onset temperature, that is, the measured boiling point. For four of these mixtures other molar fractions were also tested. Estimations of the boiling points followed the appropriate thermodynamic approach. The results revealed that the optimized condition may fail in some situations for binary mixtures, and that this fail could not always be related to the difference in the boiling points of their pure compounds. Further work is necessary in this direction.

Aspects of the thermogravimetric analysis of liquid mixtures as predictive or interpretation tool for batch distillation

“…The validity of this DSC use seems confirmed by the very similar trends observed in quite different mixtures that undergo dynamic analysis [12], interpreted by the authors in the same way as in our case. On the other hand, Troni et al [37] pointed out that even closedpan experiments (meant to yield a unique boiling point) can undisclosed the lighter component early evaporation, but not systematically nor at the expected temperature.…”

On using a Netzsch 449 Jupiter synchronous thermal analyzer to determine the boiling point of substances

“…Обе работы подтвердили возможность измерения температур плавления и кипения с помощью оборудования термического анализа. Авторы [8][9][10] изучали возможность применения ТГ, ДСК и ДТГ для определения точек плавления, кипения и давления паров различных органических веществ. По результатам работ авторы сошлись во мнении, что данным методом можно определять указанные параметры, несмотря на незначительные отклонения в значении температур от литературных данных.…”