Evaluation of the nonrandom hydrogen bonding (NRHB) theory and the simplified perturbed-chain-statistical associating fluid theory (sPC-SAFT). 2. Liquid-liquid equilibria and prediction of monomer fraction in hydrogen bonding systems

Two statistical thermodynamic models, the nonrandom hydrogen bonding (NRHB) theory, which is a compressible lattice model, and the simplified perturbed-chain-statistical associating fluid theory (sPC-SAFT), which is based on Wertheim's perturbation theory, were used to model liquid-liquid equilibria and predict the fraction of nonhydrogen bonded molecules in various hydrogen bonding mixtures. Carefully selected binary mixtures, which include water-hydrocarbon, 1-alkanol-hydrocarbon, water-1-alkanol, and glycol-hydrocarbon, were used to benchmark the accuracy of the models. Both models yielded satisfactory and often very similar results for the phase behavior of the investigated mixtures. sPC-SAFT yielded more accurate predictions, while NRHB yielded more accurate correlations, in mixtures of water with normal alkanes and cycloalkanes. In water-aromatic hydrocarbon mixtures, satisfactory correlations were obtained only when solvation was accounted for. Both models resulted in satisfactory correlations for all other mixtures, while for specific mixtures, one model may perform better than the other. Finally, both models, despite that they are based on totally different approaches for the treatment of hydrogen bonding, yielded similar predictions for the fraction of non-hydrogen bonded molecules (monomer fraction) in pure 1-alkanols and in 1-alkanol-n-hexane mixtures.