(179a) Molecular Modeling of Fluid Phase Equilibria for Ternary Mixtures With Two Or Three Liquid Phases

Multi-component mixtures that exhibit a liquid–liquid miscibility gap are of utmost importance for the oil and gas industries because of the prevalence of hydrocarbons and water in many processes.  Given the complexity of such mixtures, it is not surprising that equation-of-state-based approaches perform best for the correlation of experimental measurements but are less successful for the a priori prediction of miscibility gaps.  Molecular simulations of these multi-component mixtures with liquid–liquid miscibility gap are hampered by sampling difficulties (multiple phases must be treated explicitly, transfers of molecules between two liquid phases are much less likely to succeed, and spatial distribution of compounds in liquid phases is heterogeneous on the molecular scale) and by the lack of transferable force fields.  Here we present configurational-bias Monte Carlo simulations in the Gibbs ensemble to investigate the vapor-liquid-liquid and vapor-liquid-liquid-liquid equilibria for binary and ternary mixtures containing water, n-decane, and 2-butoxyethanol.  The predicted phase diagram is compared to experimental data [1] and the liquid-phase microheterogeneities obtained from analysis of simulation trajectories are discussed.

[1] S. Negahban, G.P. Willhite, S.M. Walas, and M.J. Michnick, “Three-liquid-phase equilibria of ternary and quaternary mixtures, water/n-decane/2-butyloxyethanol and water/n-octane/1-propanol/sodium chloride – Experimental measurements and their correlation with the UNIQUAC model,” Fluid Phase Equil. 32, 49-61 (1986).