Modeling vapor–liquid interfaces with the gradient theory in combination with the CPA equation of state

Abstract

With the final purpose of describing the important aqueous + hydrocarbon liquid–liquid interfaces, the gradient theory was combined with the Cubic-Plus-Association equation of state (CPA EOS), taking advantage of the correct representation of interfacial tensions provided by the gradient theory and the correct phase equilibrium of water + hydrocarbon systems already obtained from CPA.In this work, preliminary studies involving the vapor–liquid interfacial tensions of some selected associating and non-associating pure components (water, ethanol, n-butane, n-pentane, n-hexane, n-heptane) are presented and discussed.The good description of equilibrium properties such as vapor pressure and liquid and vapor phase densities is shown in the full range of the vapor–liquid saturation line. For non-associating components, results are compared with those from the Soave–Redlich–Kwong and Peng–Robinson equations of state.A correlation for the influence parameter is presented from which surface tensions can be obtained in a broad temperature range with average errors smaller than 1%.