Monte Carlo simulations of vapour–liquid phase equilibrium and microstructure for the system containing azeotropes

Abstract

Phase equilibrium data of the mixtures including alcohols, esters and organic acids are of first interest particularly to design and optimise biodiesel production and reactive distillation processes. In this work, vapour–liquid phase equilibrium of these systems was simulated at low pressure using Gibbs ensemble Monte Carlo method. All Lennard–Jones parameters of pseudo-atoms involved in the systems were derived from previous parametrisations of TraPPE-UA force field. The Fourier coefficients of dihedrals encountered in ethyl acetate molecule have been obtained from the quantum calculations. Using this force field, temperature-composition diagrams are well reproduced for ethyl acetate + ethanol, ethyl acetate + methanol at 70.00 kPa and ethyl acetate + acetic acid mixtures at 77.33 kPa. The transferability of this force field to mixtures in these systems is noticeable. Analysis of the microstructure for the ethyl acetate + ethanol and ethyl acetate + acetic acid mixtures was presented. We found that the hydrogen bond networks consist of autoassociation and cross-association and autoassociation occupies the main position as compared with cross association in the ethyl acetate + ethanol mixture. OC_HAc–H_HAc and OC_EtOAc–H_HAc hydrogen bond interactions play a significant role in the phase behaviours or structures of ethyl acetate + acetic acid mixture.

Keywords:

• Monte Carlo
• Gibbs ensemble
• phase equilibria
• azeotropes
• microstructure