On the D₂/H₂ adsorption selectivity of sodium decorated polycyclic aromatic hydrocarbons. I. Accurate modeling...

In the search for an economical approach to separate deuterium and protium isotopes, we have theoretically investigated the equilibrium adsorption of these diatoms onto Na-decorated polycyclic aromatic hydrocarbons: protonated coronene and, as a graphene prototype, circumcircumcoronene. We have developed accurate interaction potentials between H₂ and these substrates (within pseudo-atom or rigid-body approximations) and have solved the Schrödinger equation for the adsorbed H₂ and D₂ in order to compute the corresponding partition functions. In this way, adsorption isotherms and D₂/H₂ selectivity have been estimated providing a complete characterization of the low pressure behavior. Our results show that the pseudo-atom model is insufficient to correctly predict the mentioned properties and that neglecting the contribution of thermally excited states provides a lower bound of the exact selectivity. As for quantitative aspects, both materials have been found to afford a deuterium selectivity well above 6, the required value for industrial applications. Also, separation of spin isomers of H₂ is shown to be effective. In this respect, these substrates appear to be suitable candidates as chromatographic stationary phases, warranting additional studies on their separation capabilities at higher pressure. The theoretical framework developed for such a task and the results thus obtained are presented in a second article in this series.