(732c) Thermodynamic Modeling of Double Azeotrope - a Study of Methanol-Diethylamine Binary Mixture

"Azeotrope is a mixture of liquids which boil at a constant temperature at a given pressure.
Although such mixtures are difficult to separate, they have proven useful to overcome
various challenges such as minimization and recovery of waste of chemical processes, thus
helping build a greener world. Therefore, it renders development of a thermodynamic model
to correlate vapor liquid equilibrium conditions for mixtures exhibiting such behavior. In
general, one stable azeotrope formation occurs for a mixture for a given VLE conditions. The
property of a mixture that produces more than one stable azeotrope at a given temperature
or pressure is known as polyazeotropy. Representing the VLE data for a mixture exhibiting
polyazeotropy has been of interest for many years.

The present study focuses on the binary mixture consisting of Methanol and Diethylamine.
This mixture involves self-association between the components as well as cross association
which is why mixed deviations from Raoult's law are observed. This behavior is not
observed at low pressure for a constant temperature, but as the pressure increases double
azeotropy can be detected. This study includes the analysis of association extents (bounded
or non-bounded sites) to explain how the double azeotropes are related to the associations.
Correlating the VLE data using UNIQUAC/UNIFAC model is insufficient as it only works for low and moderate pressures. Since the system exhibits cross and self-association, Nonrandom
two-liquid (NRTL) model is also not well suited as it is does not account for specific
chemical associations. Therefore, in order to represent the given system, Non-random two liquid
activity coefficient model with association theory is used. This model combines
Wertheim's perturbation theory for associations between the constituents with the classical
NRTL model accounting for the non-idealities in the liquid phase. It regresses binary
interaction parameters and unary molecule specific parameters to provide a satisfactory
correlation for the experimental VLE data obtained from literature and successfully correlate
the VLE data for the given binary mixture for a wide range of pressures."