(257h) A Molecular Insight on the Azeotropic Phenomenon from Monte Carlo Simulations

In order to improve the separation efficiency of azeotrope mixtures, it is crucial to understand profoundly their formation mechanism form the view of molecular. This article shed an insight of azeotropic cluster into the formation mechanism of the azeotrope based on the Gibbs ensemble Monte Carlo(GEMC) simulation. The data of liquid-vapor phase equilibrium (VLE), thermodynamic properties, radius distribution functions (RDFs) and the structure of the binary azeotrope ethanol/benzene were investigated by the Gibbs ensemble Monte Carlo calculations with the united atom transferable potentials for phase equilibria (TraPPE-UA). The calculated results of VLE and thermodynamic properties present better depiction compared with data from Wilson equation and the experiments from the literature, although some deviations were observed. ‘Azeotrope cluster', as a model to describe the particular stucture of azeotrope, was clearly identified both in the the vapor and liquid phases. Balls with radius of 6.5~6.7Å and 44.5~46.9Å can be visualized to represent the ‘azeotrope cluster' in vapor and liquid phase respectively, which can be proved by the analyses of RDFs and statistics of hydrogen bonding association or other strong molecular interactions. Finally, to further explore the conditions for mixtures to present azeotropic phenomenon, the basic aggregation of ethanol molecules in the liquid phase was investigated. Therefore an inference of necessary and sufficient conditions forming azeotrope was raised and proved to be true.