(395a) Polyazeotropy for Binary Mixtures: Methanol and Diethylamine

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 behavior¹. 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 pressures². Since the system exhibits cross and self-association, Non-random two-liquid (NRTL) model is also not well suited as it is does not account for specific chemical associations³. Therefore, in order to represent the given system, Non-random two-liquid activity coefficient model with association theory⁴ 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.

References

1. Wisniak, Jaime, Hugo Segura, and Ricardo Reich. "Polyazeotropy in binary systems." Industrial & engineering chemistry research 35, no. 10 (1996): 3742-3758.

2. Aucejo, Antonio, Sonia Loras, Rosa Muñoz, Jaime Wisniak, and Hugo Segura. "Phase equilibria and multiple azeotropy in the associating system methanol+ diethylamine." Journal of Chemical & Engineering Data 42, no. 6 (1997): 1201-1207.

3. Bala, Aseel M., and Carl T. Lira. "Relation of Wertheim association constants to concentration-based equilibrium constants for mixtures with chain-forming components." Fluid Phase Equilibria 430 (2016): 47-56.

4. Hao, Yifan, and Chau‐Chyun Chen. "Nonrandom two‐liquid activity coefficient model with association theory." AIChE Journal 67, no. 1 (2021): e17061.