Equation of state associated with activity coefficient models to predict low and high pressure vapor-liquid equilibria

A simple and thermodynamically consistent method is presented to establish an equation of state for mixtures by using activity coefficient model param eters. All current solution models such as NRTL, van Laar, UNIFAC, or any o ther thermodynamic model can be used. The main feature of the method presen ted is that only a single scaling factor value determined at a given refere nce temperature is required to predict the vapor-liquid equilibria in a wid e range of temperature and pressure. The performance of the method is teste d on the prediction of the vapor-liquid equilibria at low, moderate, and hi gh pressures for six binary systems (methanol-benzene, acetone- water, meth anol-acetone, methanol-water, ethanol-water, and 2-propanol-water) and a te rnary system (acetone-water-methanol). For comparison, vapor-liquid equilib rium calculations were carried out with the Wong and Sandler method by usin g the PRSV equation of state associated with the van Laar and scaling facto rs. On the whole, it is found that at high pressures both methods give simi lar predictions but at low pressures the proposed method gives sometimes be tter results than that of Wong and Sandler method. (C) 2000 Elsevier Scienc e S.A. All rights reserved.