Modelling the thermodynamics mixtures of N2, O2, and Ar. The state-of-the-art of available models.

The optimal design of cryogenic systems for the separation of species that compose the air, mainly N2, O2 and Ar, has become a focus of attention in the development of low-CO2 emissions systems for the production of electrical energy and/or energy vectors, such as hydrogen. The pivotal action to optimize these processes and to reduce uncertainties related to the competitiveness with other separation technologies is the application of models that accurately reproduce thermodynamic and transport properties of mixtures of N2, Ar and O2. The purpose of this work is to analyse the available thermodynamic models considered as the most suitable for these systems. This paper compares the accuracy of two multi-parameter models (GERG-2008 and Bender) and of the Peng-Robinson equation-of-state, assessing their capability in calculating phase-equilibrium properties, density, enthalpic and volumetric properties change due to mixing. Moreover, it is shown the impact of inaccurate density calculations on the determination of transport properties.