Development of the AVEC model for associating mixtures using NMR spectroscopy

Abstract

AbstractCommon models for excess Gibbs energy account primarily for physical forces and do not represent strong specific interactions. However, purely chemical models neglect strong nonspecific forces and combined chemical‐physical treatments involve an unreasonable number of adjustable parameters. One way to ameliorate this limitation is to make independent measurements of the parameters by a nonther‐modynamic technique. We report an investigation of hydrogen bonding, a localized and very directional specific interaction, conducted in various alcohol mixtures using Fourier transform nuclear magnetic resonance to measure the number of complexed species in solution. A chemical‐physical association model with variable equilibrium constants has been developed. The distinguishing feature of this model is that the species in solution do not have equal probability of forming yet require only a single chemical interaction parameter determined from fitting NMR data and a physical interaction parameter determined from infinite dilution activity coefficients. The AVEC model successfully predicts vapor‐liquid equilibrium and excess enthalphy as well as liquid‐liquid equilibrium, an especially stringent test.