Azeotrope Prediction by Monte Carlo Molecular Simulation

Abstract

This article presents a methodology for checking the existence of the azeotrope and computing its composition, density, and pressure at a given temperature by integrating chemical engineering insights with molecular simulation principles. Liquid-vapor equilibrium points are computed by molecular simulations using the Gibbs ensemble Monte Carlo (GEMC) method at constant volume. The appearance of the azeotropic point is marked by a shift of the equilibrium constant from one side of the unity to the other. After each GEMC simulation, an identity change move is derived in the grand canonical ensemble to progress towards the azeotrope along the equilibrium curve. The effectiveness of the proposed methodology is successfully tested for several binary Lennard-Jones mixtures reported in the literature.

Molecular Mechanism for Azeotrope Formation in Ethanol/Benzene Binary Mixtures through Gibbs Ensemble Monte Carlo Simulation

“…Its accuracy for phase equilibrium prediction depends strongly on the initial condition for integration 46,47 and it also fails to capture the critical-point phenomenon 44,45,48 . Another method is histogram-reweighting Monte Carlo (HrMC) 49 which accurately predicts the location of azeotropic points in ethane/per uoroethane, propanal/n-pentane, and acetone/n-hexane mixtures 50,51 . However, for many other mixtures, such as acetone/chloroform, acetone/methanol, and chloroform/methanol, azeotrope prediction by HrMC was found to be rather inaccurate 52 .…”

“…One example is the Gibbs–Duhem integration (GDI) method, which was successfully applied by Pandit and Kofke to capture azeotropes modeled by different L-J model parameters. Its accuracy for phase-equilibrium prediction depends strongly on the initial condition for integration , and it also fails to capture the critical-point phenomenon. ,, Another method is histogram-reweighting Monte Carlo (HrMC), which accurately predicts the location of azeotropic points in ethane/perfluoroethane, propanal/ n -pentane, and acetone/ n -hexane mixtures. , However, for many other mixtures, such as acetone/chloroform, acetone/methanol, and chloroform/methanol, azeotrope prediction by HrMC was found to be rather inaccurate . The most widely used method in this area is the Gibbs ensemble Monte Carlo (GEMC) method, which has been applied to the VLE of a wide range of azeotropic mixtures, such as ethanol/water, methanol/ n -hexane, ethanol/ n -hexane, 1-pentanol/ n -hexane, methanol/acetonitrile, 1-propanol/acetonitrile, ethyl acetate/ethanol, and methanol/ethyl acetate .…”