(535c) Classical Behavior of Hydrogen and the Prediction of Its Mixture Properties

Molecular hydrogen is earmarked to play an increasingly important role in the global economy [1] because its combustion only results in the environmentally benign production of water. As such, there is plenty of incentive to accurately predict both its properties and those of its mixtures. Understanding hydrogen from a theoretical perspective is complicated by the fact that it is a quantum fluid, which means that theoretically rigorous first principles determination of its intermolecular interactions requires solving the Schrödinger equation with a post-Hartree–Fock method. There have been various attempts [2-4] to develop and intermolecular potential for hydrogen, however the focus has been to determine its cryogenic behavior that is affected by quantum behavior. However, many important chemical engineering applications occur at relatively high temperatures at which quantum interactions are not an important consideration. This means that incorporating quantum considerations are actually counter-productive to accurate predictions. For example, the critical properties of hydrogen that are commonly used as inputs to both theory and equation of state modelling [5] are arguably in appropriate beyond cryogenic conditions.

To address this issue, we have recently reported [6] a classical intermolecular potential that combines ab inito data for two-body interactions with a three-body potential. The potential yields accurate predictions of the second virial coefficients and pressure-volume-temperature behavior. A consequence of the potential is that yields classical values of the critical properties. This work examines the molecular simulation [7] results for pure fluids and determines the vapor-liquid equilibria of key hydrogen mixtures. It is shown that the classical potential improves the a priori prediction of mixtures by reducing the reliance on combining rules for unlike mixture properties.

1. L. F. Vega and S. E. Kentish, Ind. Eng. Chem. Res. 61, 6065 (2022).

2. P. Diep and K. Johnson,, J. Chem. Phys. 112, 4465 (2000). Erratum: J. Chem. Phys. 113, 3480 (2000).

3. T. Pham Van, and U. K. Deiters, Chem. Phys. 457, 171 (2015).

4. K. Patkowski, W. Cencek, P. Jankowski, K. Szalewicz, J. B. Mehl, G. Garberoglio, and A. H. Harvey, J. Chem. Phys. 129, 094304 (2008).

5. Y. S. Wei and R. J. Sadus, AIChE J. 46, 169 (2000)

6. U. K. Deiters and R. J. Sadus, J. Chem. Phys. (2023), submitted.

7. R. J. Sadus, Molecular Simulation of Fluids: Theory, Algorithms and Object-Orientation (Elsevier, Amsterdam, 1999).