Determination of NRTL Parameters for Aqueous Solutions using a Vapor Hold-Up Compensable Ebulliometer

Abstract

Activity coefficient equations such as the NRTL equation are widely used for examining solvent recycling processes where distillation separation is used. However, many activity coefficient parameters of aqueous systems have not been determined. Because aqueous systems can form two liquid phases according to the conditions, experimental determination is not necessarily easy. This study aims to determine activity coefficient parameters of two liquid systems. First, because a vapor hold-up compensable ebulliometer was unable to measure a heterogeneous system, it was modified. Next, the boiling points of three binary systems, namely, 2-propanol+water and 2-butanol+water, which show heterogeneous azeotropic systems, and water+n-pentyl acetate, which is not reported in available vapor–liquid equilibria data and is not a homogeneous system, were determined in a range of 40.00 to 98.66 kPa. Experimental boiling point data were satisfactorily correlated using the NRTL equation.
For the 2-butanol+water system, for which vapor–liquid equilibria and solubility data are available, boiling point data were correlated using the vapor–liquid equilibria and solubility data. Compared with using only the boiling point data, the solubility data determined were closer to the measured values. It was postulated that the NRTL parameter of the water+n-pentyl acetate system as measured was useful because measured data have not yet been reported for vapor–liquid equilibria.