Predictions of Hg⁰ and HgCl₂ Adsorption Properties in UiO-66 from Flue Gas Using Molecular Simulations
2019
Tang, Hongjian | Fang, Hanjun | Duan, Yufeng | Sholl, David S.
Adsorption of mercury species in porous materials is an attractive means to capture these species from flue gas, but the lack of reliable force fields (FFs) for Hg⁰ and HgCl₂ has made modeling adsorption of these important species challenging. We introduce a robust set of FFs to describe interactions between Hg⁰, HgCl₂, and other flue gas components and UiO-66, a prototypical metal–organic framework. Using these FFs, adsorption isotherms in UiO-66 for pure components and mixtures of Hg⁰, HgCl₂, N₂, CO₂, and SO₂ were simulated. HgCl₂ has a strong affinity for UiO-66, with a heat of adsorption of ∼60 kJ/mol, whereas Hg⁰ is only weakly adsorbed. Critically, HgCl₂ competes strongly with adsorption of CO₂; we give illustrative examples where concentrations of HgCl₂ as low as 1 ppm strongly diminish the selectivity and uptake of UiO-66 for CO₂ that would be expected for a clean flue gas mixture. These results highlight the potential importance of even trace levels of HgCl₂ in consideration of nanoporous adsorbents for CO₂ capture in practical settings.
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