“A crossover approach for the Cubic-Plus-Association Equation of State”
Abstract:
The correct representation of the thermodynamic properties of fluids is crucial in chemical and petroleum engineering. In fact, the accuracy of a model affects the sizing of equipment and control of the operation units.
In the case of the Oil & Gas industry, Equations of State (EoS) that explicitly take into account the association between molecules are used for modeling the properties of fluids containing hydrogen-bonding substances.
One of such models is the CubicPlusAssociation (CPA) EoS, which is able to correctly describe the phase equilibria of systems containing associating species, like water and methanol, far away from the critical point.
On the other hand, in the near-critical region, where the fluctuations in the thermodynamic properties become significant, large deviations from experimental data are observed.
In order to obtain a model that is capable of describing complex fluids far away and close to the critical point, we have applied the crossover procedure, developed by White and coworkers, to the CPA EoS, in which the contributions of long and short range density fluctuations are added in a stepwise manner to the free energy density of the system.
The resulting model (Crossover CPA) was applied to describe the properties of different pure and binary fluids and the results were compared to CPA and other thermodynamic models.