Scaling towards the critical point in the combined reaction/Gibbs ensemble

Polat, H.M.; Lasala, Silvia; De Meyer, Frédérick; Houriez, Céline; Moultos, O.; Vlugt, T.J.H.

doi:10.1016/j.fluid.2024.114084

Scaling towards the critical point in the combined reaction/Gibbs ensemble

Title

Scaling towards the critical point in the combined reaction/Gibbs ensemble

Author

Polat, H.M. (TU Delft Engineering Thermodynamics)
Lasala, Silvia (Laboratoire Réactions et Génie des Procédés (LRGP))
De Meyer, Frédérick (TotalEnergies; Center for Thermodynamics of Processes (CTP))
Houriez, Céline (Center for Thermodynamics of Processes (CTP))
Moultos, O. (TU Delft Engineering Thermodynamics)
Vlugt, T.J.H. (TU Delft Engineering Thermodynamics)

Date

2024

Abstract

We explore the impact of force field parameters and reaction equilibrium on the scaling behavior towards the critical point in reactive binary systems, focusing on NO ₂/N ₂O ₄. This system can be considered as a special single-component system since NO ₂ and N ₂O ₄ are in chemical equilibrium via the chemical reaction 2NO ₂⇌N ₂O ₄. We simplify the system by representing both components as single LJ particles, achieving excellent agreement with densities computed using molecular simulations in which all-atom force fields were used. We investigate the effect of force field parameters (ɛ and σ) on phase behavior and show that the critical exponent β remains constant, which means that intermolecular interactions do not affect the scaling to the critical point when the chemical reaction takes place. We also investigate the sensitivity of the reaction equilibrium constant and show that even small changes in isolated molecule partition functions lead to large differences in chemical equilibria. We show that the critical exponent β is different for systems with different reaction equilibrium constants, so a careful parameterization of β is needed for an accurate computation of critical temperatures of reactive mixtures. We perform a screening of reactive binary mixtures for a wide range of ideal gas reaction equilibrium constants, revealing key insights into the thermodynamic behavior and critical properties. Thereby we facilitate the efficient screening of reactive binary mixtures for various applications. Our results emphasize the importance of accurately parameterizing β and provide valuable insights into the critical scaling behavior of complex reactive systems.