Wertheim’s Association Theory for Phase Equilibrium Modeling in Chemical Engineering Practice

Abstract

Association and complex formation are the most important contributors to nonidealities in modeling phase equilibria. Models based on Wertheim's association theory are reviewed in the context of current industrial practice, showing great promise in resolving many of the shortcomings of the currently available models. Several pitfalls of common models are highlighted, showing the advantages of association theory. Infinite dilution activity coefficients can provide valuable insights into the liquid phase nonidealities. Trends for various mixture classifications are tabulated and explained simply in terms of "differences in molecular association". The need for a systematic procedure to characterize association parameters is cited as the most important barrier to broader implementation of these models. Improper characterizations can undermine the advantages of association theory, possibly confusing whether it offers any advantage. Resolving these issues will improve traditional small molecule phase equilibrium modeling and many other applications as well.

Efficient Implementation of Wertheim’s Theory: 2. Master Equations for Asymmetric Solvation

“…This distinction means that eq is approximate. Nevertheless, studies of the impact of association modeling on phase behavior and activity coefficients show that high precision in the donor–acceptor energy is not necessary to achieve the benefits of association modeling; furthermore, it is recommended that characterization of these energetic parameters follow systematic trends that are supported with multiple inferences such as spectroscopic data and infinite dilution activity coefficients Equation dovetails nicely with this recommendation because individual donor and acceptor energies can be correlated with measures of acidity and basicity derived from Kamlet–Taft characterizations, , MOSCED activity coefficients, and COSMO-RS/SAC ,, sigma profiles …”

“…Overall, this is a preliminary indication that the solvation model provides a better physical basis for treating these systems. Lira et al provide a deeper analysis of these issues, especially in dilute regions …”

Current Practices and Continuing Needs in Thermophysical Properties for the Chemical Industry

“…61 Huber et al 62 describe the REFPROP EOS for reference quality properties of high volume chemicals and Alsaifi and Elliott describe a methodology to avoid artifacts in noncubic EOSs. 63 Articles by Lira et al, 46 Lira et al, 48 Fouad et al, 64 and Elliott 65 describe recent developments regarding Wertheim association theory. These are followed by articles on multisolvent electrolytes phase equilibrium by Wang et al, 111 Djamali, 67 and Yang et al, 68 physical property models for adsorption and nanopore, 69,70 molecular simulations for bioseparations, 66 mesoscale modeling of micellization and adsorption of surfactants, 71 use of micelle formation for bioseparations, 72 and non-electrolyte product properties.…”

Thermophysical Properties for Chemical Industry

“…Nevertheless, both of these approaches are limited in their modeling of self-and crossassociation effects. 3 Molecular simulation and thermodynamic perturbation theory were also recognized then as tools that would help to make progress more systematic.…”

“…Local composition models for liquid-phase activity coefficients or mixing rules based on Gibbs excess functions or density-dependent local compositions in equations of state are still among the most accurate approaches in process calculations and modeling, as well as product development. Nevertheless, both of these approaches are limited in their modeling of self- and cross-association effects . Molecular simulation and thermodynamic perturbation theory were also recognized then as tools that would help to make progress more systematic.…”