Recent advances with association models for practical applications

Abstract

Association models like CPA and other SAFT variants have found widespread use, especially over the recent 30 or so years, and this is not limited any more to universities and researchers. Industry is beginning slowly to adopt such models for some applications and a few of the association models are now provided by commercial simulators. Association models account explicitly for hydrogen bonding (and other complex) phenomena and for this reason they are potentially more useful and more successful than traditional models like cubic equations of state and activity coefficient models. Still, for practical applications all models are judged by their results and these depend on availability of experimental data, the number and type of adjustable parameters and the performance of the models for phase equilibria and occasionally also for other properties. We will consider four case studies in this work which will illustrate some of the capabilities and limitations of these association models in different applications. We will offer a "model developer's" point of view showing in several cases all stages of model development in order to illustrate what worked, what didn't and how it was corrected (when possible). The "physics" and "application" aspects of the models will be in all cases discussed. All results will be shown with the CPA equation of state, although we expect that the overall conclusions will be the same for a wide range of association models.

A Statistical Associating Fluid Theory Perspective of the Modeling of Compounds Containing Ethylene Oxide Groups

“…The pure-component parameters of most SAFT models must be regressed from available experimental data, commonly the liquid densities and vapor pressures of the pure compounds in an extensive temperature range. However, the inclusion of additional data such as second-order derivative properties, − monomer fractions, − and/or enthalpies of vaporization may improve the model’s robustness and accuracy.…”

“…Several extensions, modifications, and improvements of the SAFT approach have been developed over the last few decades. Naturally, an exhaustive description of such modifications is outside the scope of this review, but a number of monographs , and excellent reviews about SAFT, its capabilities, and applications are available in the literature for further reading. ,− …”

“…112,113 An analysis of the references contained in Table 2 shows that different association models have been used for the thermodynamic modeling of glycols. However, as shown in Figure 6, more than half of the works published in this topic were carried out using the CPA EoS, in part thanks to the extensive work of Kontogeorgis and co-workers 25,26,81 that have shown a long-term interest in gas-hydrate related systems.…”

“…As seen in Figure , a large number of thermodynamic models are available with dozens of different activity coefficient models and equations of state (EoSs) reported in the literature, the choice of the most adequate representing a cumbersome challenge for the design engineer not specifically trained in applied thermodynamics. Among these models, advanced molecular-based EoSs, derived from the statistical associating fluid theory (SAFT), − have found widespread use in academia and a progressive adoption by industry . These models, by being able to explicitly account for strong, short-range, and highly directional forces like hydrogen bonding, and other complex effects, are potentially more accurate and physically meaningful than the more traditional cubic EoSs or activity coefficient models when applied to the description of a wide range of fluids including water, glycols, and glymes.…”

“…Among these models, advanced molecular-based EoSs, derived from the statistical associating fluid theory (SAFT), 22−24 have found widespread use in academia and a progressive adoption by industry. 25 These models, by being able to explicitly account for strong, short-range, and highly directional forces like hydrogen Table 1. Families of Compounds Containing EO Groups Figure 1.…”