Calculation of Vapor-Liquid Phase Diagram of the Binary Mixture of Methanol and Benzene using Gibbs Ensemble Monte Carlo.

Abstract

Azeotropes have been always remained the topic of interest due to the challenges they pose in their separation. Although experimental studies have been done with the infrared spec- troscopy (IR), Raman spectroscopy, mass spectroscopy (MS), X-ray diffraction, inelastic neu- tron spectroscopy, nuclear magnetic resonance spectroscopy (NMR), and Fourier-transform infrared spectroscopy (FT-IR) setups to know the reason behind this unique behavior of boiling at a constant temperature, these experimental studies can only infer the results from the data obtained. However, they cannot provide the molecular-level picture of what happens at the azeotropic point. To study the molecular mechanism and the role of ther- modynamics in the formation of azeotropes, molecular simulations are the most helpful tool to explain the macroscopic picture using the microscopic properties of the underlying ener- getics. This study employs the Metropolis Monte Carlo method to investigate the molecular structure at azeotropic composition. We have used the united atom-transferable potentials for phase equilibria (TraPPE-UA) force field to model the methanol/benzene mixture (pos- itive azeotrope). Various analyses are performed to support the accuracy of the force field. The temperature-composition phase diagram and azeotropic point have been predicted us- ing Gibbs ensemble Monte Carlo simulations, with good agreement from experimental data. Further, the TraPPE-UA force field is implemented in the molecular dynamics software to study the effect of temperature in the azeotropic formation. The force field’s accuracy for modeling the methanol/benzene system is checked by comparing the energetics with Monte Carlo results.