Tracing Experimentally Compatible Dynamical and Structural Behavior of Atmospheric N₂/O₂ Binary Mixtures within Nanoporous Li–LSX Zeolite: New Insights to Influence of Extra-Framework Cations by MD Simulations

Abstract

Along with available adsorption isotherms and uptake kinetic data, microscopic knowledge of the guest self-diffusion and intracrystalline movement of the simple air binary mixture of nitrogen (N2) and oxygen (O2) within Li–LSX zeolite is needed to optimize the design and to reach a breakthrough high-efficiency of air separation process based on the selective adsorption in this zeolite. In the current work for the first time, an all-atom molecular dynamics (MD) simulation is used to study the average single-particle dynamics, self-diffusion, and microscopic structure of the atmospheric binary gaseous mixtures of N2 and O2 in Li–LSX zeolite at temperatures between (260 and 700) K. The common order of magnitude of the computed guest self-diffusion coefficients at different temperatures is in the range of 10–9 - 10–8 m2·s–1 and corresponding activation energies obtained using the Arrhenius equation varied in the range of ∼0.6 for O2 to 1.6–3.3 kcal·mol–1 for N2 in simulations with mobile and with fixed extra-framework Li+ on SIII sites (Li–III), respectively. Present results provide some new molecular-level insights into the link between the behaviors of the pendulum-like motion of Li–III with the guest molecules. Results show that O2 guest molecules freely move into the supercages and channels of the zeolite without any attachment to the key sorption cationic sites and the behavior of O2 is independent of the fixed or mobile Li–III situation during of simulations. In contrast, the oscillatory motion or immobility of the Li–III cation is found to have a surprisingly large influence on the intracrystalline N2 self-diffusion, the local (N2–Li–III) structural correlation, and the mean time of attachment of N2 to Li–III. The different observed adsorption behavior of two guest components was previously connected to the difference in their relative values of permanent quadrupole moments which causes different guest–Li–III affinities. These are well explained by a microscopic structural and dynamical analysis in current study. O2 component diffuses faster than N2 within the nanoporous Li–LSX zeolite, especially with a greater relative diffusivity difference for simulations with fixed Li–III at relatively low temperatures which correspond to favorable selective adsorption conditions. The computed O2/N2 diffusion selectivity ratio increases with decreasing temperature.

Mineralwasser – voll die Härte

“…Wasserenthärter in Waschmitteln wie Zeolithe oder Komplexbildner wie EDTA (Ethylendiamintetraacetat) in Shampoos sind Zusatzstoffe, um Calcium‐ und Magnesiumionen abzufangen, bevor sie mit Seifen fallen können. In den dreidimensionalen Strukturen der Zeolithe binden Calciumionen bevorzugt in drei Bereichen der Alumosilikate [9; 10] und verdrängen dabei jeweils zwei dort vorher gebundene Natriumionen. Natriumionen wiederum bilden mit so gut wie nichts schwerlösliche Salze (ausgenommen Uranate [11] … doch dann wären graue Flecken auf der Wäsche nicht mehr der eigentliche Grund zur Sorge).…”

Hydrogen Storage, Magnetism and Electrochromism of Silver Doped FAU Zeolite: First-Principles Calculations and Molecular Simulations

“…In terms of theoretical/computational researches, molecular simulations with Monte Carlo method have been performed in order to predict the preferable sites, isotherms and isosteric heat of adsorption, as well as to investigate the separating mechanism for atmosphere gas binary mixtures in Li-LSX zeolites [ 12 ]. The recent literature reviews indicate little Monte Carlo research, especially for the equilibrium adsorption properties of N 2 , O 2 and H 2 in nanoporous Li-LSX zeolites [ 4 , 13 ].…”