Crossover or cross-association: the impact of different phenomena in the modeling of CO2 and an associating molecule using the CPA EoS
Abstract:
Carbon dioxide is an essential compound not only for industrial purposes but also due to its relationship with global warming.
Therefore, understanding the phase behavior of this gas with systems containing associating molecules is of key importance for our society, albeit the challenges regarding the prediction of the properties of such systems using traditional thermodynamic models, e.g. equations of state (EoS).
The modeling of the thermophysical properties of CO2-containing mixtures has improved drastically is the last decades. Different approaches have been successfully applied with the Cubic-Plus-Association (CPA) EoS, using one of the three features:
1) the addition of an explicit term taking into account quadrupolar effects
2) treating CO2 as an associating molecule
3) taking into account solvation effects between an associating molecule and CO2.
Although accurate results are obtained far away from the critical region, these approaches predict incorrect phase envelopes and critical lines of the mixtures, indicating that additional corrections are necessary.
In this work, a recursive method to incorporate density fluctuations was applied to CPA, with the aim to improve the behavior of the model in near-critical regions. The classical and crossover equations are compared in an attempt to answer what is required to improve the knowledge concerning the global phase behavior of mixtures with CO2 and an associating molecule.