An explicit hydrogen-bonding non-random lattice-fluid equation of state and its applications

The representation of hydrogen-bonding contribution by Huang and Radosz or by Veytsman involves terms that require implicit computation when more than one type of bonds is present. To reduce the computational burden associate d with the solution of a set of nonlinear implicit equations, a free energy expansion method was proposed for Veytsman statistics in the present study . Based on the normalized Veytsman statistics, the Helmholtz free energy fo r association was expanded around a reference value. The expanded free ener gy was compared with rigorous values and found to closely approximate the o riginal term. The lattice-compatible expanded Veytsman term was then combin ed with the explicit non-random lattice-fluid model of present authors to g ive the explicit free energy expression for hydrogen-bonding non-random lat tice-fluid. Parameters for the model are segment number and interaction ene rgy for physical interaction, and association enthalpy and entropy for hydr ogen bonding. For a binary mixture, a binary parameter is needed. To assure the consistency, thermodynamic properties such as pressure and chemical po tential were derived from the expanded Helmholtz free energy. Calculated va por-liquid equilibria using the expansion for alkane-alkanol mixtures were found to closely agree with experimental values and with rigorous calculati on results. (C) 2001 Elsevier Science B.V. All rights reserved.