Advances in the correlation of thermodynamic properties of binary systems applied to methanol mixtures with butyl esters

Abstract

This work analyzes the utility of a new model to correlate thermodynamic properties of solutions, the foundations of which have been published in a previous study. The model is applied to a set of experimental data for several properties of binary systems of methanol with four butyl alkanoates (vapor-liquid equilibria at p = 141.32 kPa and excess enthalpies and volumes at 298.15 and 318.15 K). Vapor-liquid equilibrium data (VLE) indicate that the four binary systems deviate positively from Raoult's law and do not present azeotrope. Excess enthalpies (hE) are positive for the entire range of compositions and decrease regularly with increasing length of the ester chain, with (a,hE/A,T)p,x > 0. The excess volumes (vE) decrease regularly with the length of the acid chain; they are positive for the binary systems of methanol with butyl (methanoate, ethanoate, and propanoate) and become negative for the system with butyl butanoate, with (a,vE/A,T)p,x > 0. The new model can be used to obtain a satisfactory correlation for Gibbs function gE = gE(p, T, xi), and for its derivatives. Correlation procedures for the data are described for the stages (x, hE) a' [x, gE(T)] for the isobaric data reported here and (x, vE) a' [x, gE(p)] for isothermal data reported in the literature. The new method allows a better correlation than the one obtained with the classical models of Wilson, NRTL, and UNIQUAC. We also present a unique correlation of all the properties of the methanol + butyl ethanoate system in the form of an analytical expression I(p, T, x, y) = 0 and conclude that, on the whole, its implementation can be considered an advance in the data treatment of the properties of liquid solutions. © 2010 American Chemical Society.