Examination of the liquid-liquid interfacial properties of water + alcohol mixtures from computer simulation

The precise knowledge of liquid-liquid interfacial properties of aqueous mixtures of alcohols is key in different chemical and petrochemical fields, including chemical, petrochemical, and environmental engineering. Interfacial... [ view full abstract ]

The precise knowledge of liquid-liquid interfacial properties of aqueous mixtures of alcohols is key in different chemical and petrochemical fields, including chemical, petrochemical, and environmental engineering. Interfacial mass transfer unit operations such as liquid extraction or interfacial chemical reactions in chemical engineering, phase wettability or capillary pressure in petrochemical engineering, or removal of contaminants in aquifers and groundwater remediation in environmental engineering, are only few examples of the importance and broad applications of systems for which very limited knowledge of liquid-liquid interfacial properties is available. In this work, we use molecular dynamic simulation to predict the interfacial properties of water + primary alcohols that exhibit liquid-liquid immiscibility phase behaviour. Water is modelled using the well-known TIP4P/2005 water model and alcohols (from 1-butanol up to 1-octanol) are described using the original TraPPE models. In particular, we have considered the temperature-dependence of the most important interfacial properties of these mixtures, including density profiles, phase coexistence diagrams, interfacial thickness and interfacial tension as functions of temperature at fixed pressure. Predictions from computer simulations carried out in the PN_zT ensemble are compared with experimental data taken from the literature. We focus particularly on the prediction of the interfacial tension of the mixtures as the temperature is varied. Surface tension increases with temperature and reaches a maximum value (related with the maximum tie line in the liquid-liquid equilibrium). At higher temperatures, the interfacial tension decreases with temperature. In addition to that, the surface tension increases as the molecular weight of the molecular chains is larger. Predictions from simulation and experimental data are compared and discussed in this paper.