Enhanced quantum sieving of hydrogen isotopes via molecular rearrangement of the adsorbed phase in chabazite

Abstract

Adsorption isotherms of H2 and D2 in pure silica chabazite at 47 K show an unexpected step associated with an increase of the D2/H2 adsorption selectivity due to molecular rearrangement.

New force field for GCMC simulations of D2/H2 quantum sieving in pure silica zeolites

“…Worth noticing that the adsorption selectivity of D2 towards H2 sharply increases from the same filling, as shown on figure 5. In a recent communication 29 , we have shown, by analyzing the density profiles of molecules adsorbed in the cages calculated by GCMC, that this step is the result of a molecular rearrangement of the adsorbed phase induced by confinement effects. Below 18 molec.uc -1 , the H2 and D2 molecules are adsorbed in the middle of the cages with a low selectivity (i.e., in similar proportion as in the gas phase).…”

“…The zeolite was prepared using the method described by Díaz Cabañas et al 31 . These materials have been extensively characterized by XRD, FTIR, SEM, NMR and N2 adsorption in our previous works 29,32,33 . Silica MFI is perfectly crystallized with right morphology and microporosity and without silanol defects.…”

“…However, these simulations are compared only with adsorption data of single components measured on few zeolites (NaX, Rho, silicalite-1, Si-LTA) at 77 K or higher temperatures. As far as we know, only few works report a comparison of simulated and experimental adsorption selectivities below 77 K. Probably this is due to the lack of coadsorption experimental data 22,28,29 . Therefore, the achievement of new coadsorption experiments of hydrogen isotopes below 77 K is also an opportunity to test the force fields presented in the literature and their transferability among zeolitic structures having different pore geometry, but the same chemical composition.…”

Enhancement of D2/H2 Selectivity in Zeolite A through Partial Na–K Exchange: Single-Gas and Coadsorption Studies at 45–77 K

“…Given the size of the hydrogen molecule (~ 3 Å), the zeolites with 8 member rings (8MR) having pore openings of ca. 4 Å present a potential interest for the separation of hydrogen isotopes as follows from our recent studies of CHA zeolites which also contain 8MR 5,6 . Among the cation-rich zeolites having small pores LTA type materials are one the most attractive type of zeolites due to special structural features.…”

“…3 Given the size of the hydrogen molecule (∼3 Å), the zeolites with eight member rings (8MR) having pore openings of ∼4 Å, present a potential interest for the separation of hydrogen isotopes, as follows from our recent studies of CHA zeolites which also contain 8MR. 5,6 Among the cation-rich zeolites having small pores, LTA type materials are one the most attractive type of zeolites due to special structural features. Na-LTA structure can be described as an assemblage of α-cages, having the composition Na 12 Al 12 Si 12 O 48 in which the cations occupy three different positions 7 (Figure 1).…”