0000000000277121
AUTHOR
Mathieu Macaud
New force field for GCMC simulations of D 2 /H 2 quantum sieving in pure silica zeolites
International audience; We report a study on adsorption and coadsorption of H2 and D2 in FAU, MFI and CHA pure silica zeolites having different pore sizes and shapes. Adsorption capacities, selectivities, enthalpies and entropies are determined by combining experiments and GCMC simulations. We show that the force fields available in the literature cannot predict the adsorption equilibria below 77 K with sufficient accuracy. Here we propose a new force field adjusted by using our experimental data obtained for the pure silica MFI zeolite at 65 K and 77 K. With this new force field, it is possible to predict the adsorption and coadsorption equilibria on the three zeolite structures in a tempe…
Adsorption of hydrogen isotopes in the zeolite NaX: Experiments and simulations
Abstract Among the different methods to separate hydrogen isotopes one is based on the physisorption at low temperature (below 100 K) where quantum effects induce a particular behavior. In the present work, we study the adsorption of single H 2 and D 2 on the zeolite NaX by combining experiments (manometry) from 30 to 150 K and molecular dynamics simulations at 40 and 77 K. Simulations also include the adsorption analysis for T 2 . Adsorption on NaX membranes is simulated and quantum corrections are introduced by using the well-known Feynman–Hibbs approach into the interaction potentials. Experimental adsorption isotherms are reproduced by using the Toth equation and it is shown that the ad…
D2 and H2 adsorption capacity and selectivity in CHA zeolites: Effect of Si/Al ratio, cationic composition and temperature
International audience; The work deals with the effect of composition of CHA zeolites on the adsorption and separation of H2 and D2 under cryogenic temperatures. In the first part of this work the effect of Si/Al ratio and cationic composition on single gas adsorption of H2 and D2 was studied at 77.4 K. It was found that the adsorption capacities increase with Al content up to Si/Al = 2.1. Unexpectedly, Na-CHA zeolite with the highest Al content (Si/Al = 1.1) adsorbs only negligible amount because of the collapse of the zeolite structure upon dehydration at 400°C. The Na-and Li-containing chabazites with Si/Al = 2.1 possess similar adsorption capacities. In contrast, progressive replacement…
Quantum Effects on the Diffusivity of Hydrogen Isotopes in Zeolites
The molecular sieving of H2 and its isotopes produced by nuclear plants is a long-standing research where some adsorption processes are well identified. However, some mechanisms governing the diffu...
Enhancement of D 2 /H 2 Selectivity in Zeolite A through Partial Na–K Exchange: Single-Gas and Coadsorption Studies at 45–77 K
International audience; We report D2/H2 adsorption selectivities under cryogenic temperatures (45-77 K) in Na and K-Na exchanged zeolites A (LTA structural code) measured by co-adsorption technique. These values are systematically compared with Ideal Adsorbed Solution Theory (IAST) predictions based on the single gas adsorption isotherms. For NaA zeolite the evolution of the selectivity as a function of total pressure and gas mixture composition at 77 K shows ideal behavior. In contrast, as temperature decreases, D2/H2 selectivity rises exponentially and its values can no longer be predicted by IAST. We found that in these conditions the evolution of the selectivity can be described by a si…
Enhanced quantum sieving of hydrogen isotopes via molecular rearrangement of the adsorbed phase in chabazite
Coadsorption experiments reveal an unexpected increase of the D2/H2 selectivity with loading in pure silica chabazite at 47 K. This effect is correlated with the appearance of a step in the adsorption isotherms of H2 and D2. Grand canonical Monte Carlo simulations show that this phenomenon is related to a molecular rearrangement of the adsorbed phase induced by its strong confinement. In the case of a H2 and D2 mixture, this rearrangement favors the adsorption of D2 having a smaller size due to quantum effects.
D2/H2 adsorption selectivity on FAU zeolites at 77.4 K: Influence of Si/Al ratio and cationic composition
Abstract Equilibrium D2/H2 adsorption selectivity was determined at 77.4 K below 1000 hPa for a series of FAU type zeolites X exchanged with different cations (Li+, Na+, K+, Mg2+, Ca2+, Ba2+ and Mn2+). In addition NaY, DAY (dealuminated Y) and pure silica CHA and MFI zeolites were studied. Two experimental approaches were used to determine the D2/H2 adsorption selectivity: direct determination at the thermodynamic equilibrium from manometric coadsorption experiments and calculations by Ideal Adsorbed Solution Theory (IAST) from single gas adsorption isotherms. While these two approaches are not in quantitative agreement, they reveal similar trends. At low loading ( MnX > LiX > CaX ≈ NaX > …