The use of molecular orbital calculations to describe the phase behavior of hydrogen-bonding mixtures

Abstract

In previous studies we have used Hartree-Fock theory and density functional theory to compute the enthalpy and entropy changes of dimerization for methanol and a number of small carboxylic acids. We have shown that by using these results in a physical equation of state, the statistical associating fluid theory (SAFT), we are able to model the phase behavior of these pure hydrogen-bonding compounds with a reduction in the number of adjustable parameters; in this study, we use the pure-component parameters derived from the results of our molecular orbital calculations to describe the phase behavior of mixtures containing one associating and one nonassociating compound, again using the SAFT equation of state. We show that the use of the pure-component SAFT parameters derived from our quantum-mechanical calculations results in correlations of mixture VLE data with no loss of accuracy, and frequently with improved accuracy, compared to the original parameters reported for use with the SAFT model.